A 12 ft. FEATHERLITE conversion

[Prem]

When you post something in the future you may want to add more pictures or other details,
I looked over some of your older stuff and 30-40% of the links are dead.

Jerry,

Websites and their photos expire/get taken down. Nothing I can do about that.

Add more pictures? ME?




Coming into the 3rd largest city in AZ. Those aren't buildings in the distance. They're clusters of RVs camped out in the desert.

[MtnDon]

~~

And what is Tiger foam? Are you saying you got mold from placing foam boards in without securing them and the condensation collected between the foam and the exterior?
** Tiger Foam = a brand name
** Yes, IF foam boards placed inside against the aluminum skin have any edge gap, moisture in the form of water vapor can make its way in there and condense on the cold metal. So it sits there between the alum and foam and can cause issues.
~~~~~~~

I am not following your caulk plan.

The moisture prevention plan is based on preventing water vapor from touching the interior face of the aluminum skin.

If closed cell spray foam is sprayed on the interior that does it.

If someone uses sheet foam, cut to fit between the ribs, the seams between the rigid foam and the ribs must be sealed to prevent water vapor intrusion. That can be done with foam-in-a-can, like Great Stuff. That could also be done with caulk, that is compatible with foam. My method would be to first apply a bead of caulk to the skin around the opening and then place the foam sheet/block in there. The caulk will seal the perimeter against the skin. That seals the outside face. Then another bead of caulk around the "inside" face of the foam to rib joint. Two seals with a skinny air space between them. I like this a bit because I hate handling the uber sticky foam-in-a-can stuff.

Hope that clears that up some.

~~~~~~

I am contemplating having CarMate build mine with the plywood next to the aluminum skin and then adding foam boards glued to the plywood between the wood studs and then using great stuff and insulation tape to fill the gaps and tidy it up. Then adding plywood over the insulation followed by wainscoting/beadboard.

I am curious whether the plywood/aluminum interface would experience any rot/mold/undesirable reaction over time.

The plywood on the outside with the skin on top is an excellent method, IMO. The plywood acts as a "buffer zone" between the interior and skin. The plywood will be warmer than the metal skin. Placing foam sheets in the wall cavities and sealing them 100% adds another layer that will be warmer than the skin (when it is cold outside).

IF the foam is installed properly (airtight) there should no problem with the plywood against the inside face of the aluminum skin. Unless there is a leak in the aluminum skin or a skin seam. But that is another issue.

I have to go to town for some things... I have more to add to this later.

[Prem]

Where to have the best winter ever:

[hikediveexploregirl]

Thanks Prem and MtnDon! I believe I will confirm how the plywood/exterior interface is bonded.

I believe that if I go that route I will run some cable housing (brain fried and can't think of the term) and then spray foam it all followed by another layer of plywood. That way I can keep my cables out of the sprayfoam.

I hate mold. What a pesky thing...except for penicillin...

[MtnDon]

MtnDon

In your all spray foamed trailer - would some of your wiring be encased inside the foam ??
In my case it would be because I have at least 20+ exterior lights & cameras.
This I would see as a drawback to solid sprayed foam ?

Jerry

Wiring:
In a home where foam is sprayed into the cavities, against the exterior sheathing, there is no special requirement to encase the wiring (or the plumbing or gas) in anything. The foam is sprayed over it and that is that. The only advantage to running the wiring in a trailer through some sort of conduit would be to make it easier to run a new wire at some future date. If that is the plan then also run a string in the conduit to make running a new wire, not just a replacement, easier.

MtnDon

I'm also a little confused with your moisture Thesis

Jerry

How can I expand or fill in the holes? What area or thoughts? Glad to help with that.


Does it help to explain that what we are trying to do is to keep any surface that may be contacted by interior air, above the dew point temperature?

Example: Assume we have a poorly or non insulated wall. Last night the air temperature inside our cabin was 71 F and the humidity was 15% The dew point was 21 F. I was not there but ain't telemetry wonderful! That means that anything that had a temperature of 21 F or less would likely have condensation on it. The exterior temperature was 43 F so we were fine. If on the other hand the temperature outside was 5 F and we had the same interior conditions and had a wall skin that the interior air could contact, we would almost certainly have water condensing in that wall. That used to happen all the time in our old RV's that had single pane glass windows. The glass would fog with condensation as would the aluminum window frames. Now we have windows that are insulated double pane and window frames with thermal breaks. Well, "we" don't but they are available.

It can get tricky because a change in air temperature also affects the relative humidity.

So by thoroughly and completely sealing the interior air from the inside face of the aluminum skin using foam of some kind along with whatever caulks and sealants, we remove the possibility of condensation on the aluminum.

Hope that helps.

[hikediveexploregirl]

Conduit is the magic word! I could only come up with coaxial and well...that is a whole new can of words.

Being a "clean" engineer I like being able to make wiring changes easier and cleaner. In my salt water aquarium build I used a string with a washer on each side to weigh it down. Worked great to feed new lines!!

[OverTheTopCargoTrailer]

Hi MtnDon

Im just giving you some JAZZ... one needs air to transport the moisture. So my point was if the cavity was 98% filled with foam.... Ridged or sprayed.
THEREFORE....only a very small or limited amount of air can get in, assuming of course no grand canyon volume of air circulation through the cavity
so I would assume less air volume = less condensation. Just as if I would press foam against your RV glass - the area of solid contact with the glass would have less or no condensation.

While about 30% of heat loss is due to circulation inside the walls, electric outlets, ceiling lights, eves, windows etc....
I have left some sections accessible & am interested to see exactly what happens.
I have 6 = 120 mm fans where covers can be removed to provide mechanical air flow as needed.
I can also tell you for sure there is air between the exterior skin & alum siding as the sheets are only 4ft wide.

While your & Prem's method of spraying foam is surely more effective, I see some drawbacks for me due to my extensive exterior lights & wiring I don't want it to be incased inside the foam.
also if the was a problem with the wiring its harder to find & may increase the heat load to the device ?
Time this spring will tell if it is good enough ?

My feeling is many RV's rot from the inside out - more then from exterior leaks, if used in cold weather.

Jerry

[Prem]

FYI: You three are cracking me up.

Engineering, hiking, diving, exploring Girl wrote the best one of all:

and well...that is a whole new can of words.

Thanks for making my day. Now I have to go teach a Spanish class for the next two hours...a whole can of foreign words.

[hikediveexploregirl]

Prem,

I figured screwed up "words" was much better than screwed up "worms"!!

And if you could have pictured me at my desk trying to conjure up the word "conduit" when all my brain could locate was "coaxial"...that really would have made you laugh!

Of course, I can't discuss this project with "normal" folks for fear they will commit me to the insane asylum where all "over planners" and "over engineers" go to ponder their next version in peace.

[OverTheTopCargoTrailer]

I know exactly how you feel , lots of people sh** bricks

When I tell them after working in Silicon Valley for 30 years
I'm sooooo freggin poor , i can't even afford an RV & camping fees so I will be
Forced to retire into a cargo trailer
And live on the streets - like a bum in a 1970 Winnebago

It really shatters their illusion of wealth & I milk it for every penny it's worth.


Jerry

[hikediveexploregirl]

Try being a GIRL! Despite many very successful projects I still get the "you can't do that" stare.

So, I shall do it...and I shall smirk when they say "wow".

Of course I have threatened that the next person who says, "you should just buy a travel trailer" will promptly receive my size 8.5 shoe in their mouth.

[Prem]

Wow Engineer Girl, you can kick high! From years in karate and ballet before that?

You *are* a rare and formidable character here. (We're all characters here, aka abnormal, DIY RVers.) So in case nobody has said it, "Welcome to the forum."

P.S. I also like your use of the subjunctive:

"If it were easy then everyone would do it."

[revorunner]

My motto is.....Do your own thinking independently. Be the chess player, not the chess piece.Who cares what everyone else thinks! Besides us on this great forum of coarse. Go Girl Go!

[Prem]

Wisdom! A keeper!

Be the chess player, not the chess piece.

Thanks.

[hikediveexploregirl]

Revorunner,

I always say, "Well, I am 'just a girl'"... And with a smirk I walk away!!

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