How to strengthen frame, insulate under trailer

[notoriouskelly]

1.Floor feels spongy under my 300 lbs (so how will it react to 800 lb quad?)

I pulled floor board and see a large gap with no support.



Love to do something myself without paying a welder.

I'd just screw in some 2x6's sideways if both beams had the lip, but every other beam has lip at top.



Any recommendations?

2. I'd like to add insulation underneath that won't come off in chunks from rocks/debris, weather etc.
What kind would you use and how to put it in?

Thanks!

[8ball_99]

Is the gap really 48" between supports. Thats a little odd. Most of the time they aren't more then 24-30" tops.. If it were me I'd weld in another joist...

[notoriouskelly]

48" to center, but the other gap is more like 68" with only plywood to support it.

If it's spongy when new, imagine when it gets wet and starts rotting.

I believe the whole trailer is like that so I'll be pulling all the boards.

[bc toys]

with that span I would get some C channel or L iron [better known as angle iron] and weld then in to cut down the span no more then 24''

[8ball_99]

48" to center, but the other gap is more like 68" with only plywood to support it.

If it's spongy when new, imagine when it gets wet and starts rotting.

I believe the whole trailer is like that so I'll be pulling all the boards.

Yes I'm sure is spongy. My trailer the floor joists are 16" on center and even with that the floor isn't rock solid. I think It cost me an extra 75 bucks for them to put them on 16" center vs the standard 24" on center. 48" on center is not correct, My guess is the guy welding up the frame just forgot to put one in. I've looked at a LOT of cargo trailers and 24" center is pretty standard even with the dirt cheap ones. Only way to really fix it is to weld supports in. I would not want to try and bolt wood to the metal frame to add a brace. One of the main reasons to have a cargo camper is because of the all metal construction..
BTW how thick is the floor. It looks thin in the picture. It might just be the angle. Most come with 3/4 plywood for flooring. Some treated some not. I myself would only have treated!

[notoriouskelly]

Thanks, I'm bringing it to the welder on Monday.

The large gaps are 68" wide and the between beams is 48" wide with hole being 23 3/4".

So no wonder the whole floor is flexing:



Those wide strips are skinny metal just for screwing in cargo straps - not weight-bearing. So the untreated plywood is the only thing between cargo and the road

All front beams are rusted



and a couple side beams.

Duct tape peeled paint right off a top beam:



Oh well, I guess that's the difference between my $5,000 trailer and a $10,000 one

[8ball_99]

Oh I see what your saying. Your joists are at 24 center but the metal straps across the top have a gap. Honestly that doesn't matter most trailers mine included don't have those metal strips. I thought you were saying your joists them selves were 48" apart

[Glenlivet]

You don't need more metal cross pieces, looks like you could fix/improve the floor strength greatly with just a table saw and some common dimension lumber.
I'd do like you said earlier, measure how high it is from one of those nice bottom flanges on the cross metal beams, to flush with its top, where the flooring wood is screwed to.
Set the table saw fence and rip some common 2x whatever lumber into strips that wide. Now measure the length between one metal beam edge to the next facing metal beam edge, and cut two of your new wood supports that long. (sand the lower edges where the piece will go into the bend of the metal beam, so that it fits nicely)

Place the newly made pieces where they'll divide those big spans into thirds, or better. Once they are all laid in there put the floor wood back in place and screw it to the metal as it was, and screw it with 1 1/2" or so wood screws, to each of your new supports.
Done. Cheap. Strong.

Edit: Just checked under mine and it's flanged on one side only. Still some edge-on runners screwed to the underside of the floor would stiffen the heck out of the floor.

I'd do what you said already.

[norcal2]

Id caution using wood frame members underneath...i have another trailer..after a few years the rocks and dirt sandblast the paint and material off the frame members underneath...wood frame members would disintegrate over time, the floor is higher and is not exposed to the gravel, dust, dirt off the road..just my 2c

[notoriouskelly]

Oh I see what your saying. Your joists are at 24 center but the metal straps across the top have a gap. Honestly that doesn't matter most trailers mine included don't have those metal strips. I thought you were saying your joists them selves were 48" apart

My bad - it is 24" to center but that gap is 68" wide, so I'm heading to welder Monday to price options.

I wanna get this done so I can move on

Thanks for the tips!

[notoriouskelly]

Welder hooked me up for $295 (plus tip)

Helped me get boards in and out of trailer, welded braces, 10 cans of undercoat rubberized spray to beef up underside and bracing against elements.

Before and after pics:

Big Gaps


Braced floor

(There's bracing under the wide strips)

Gaping 68" rectangular hole


Squared strength


Cursory spray


More thorough coating after


Now I can get on with the project!

[Glenlivet]

That looks a lot stronger notoriouskelly.

[surfdog]

Well Done! MUCH stronger for the Quad.

Planning to do anything with the rust on those supports? Not sure that it (really) matters structurally,
since it may be just surface rust, but I didn't like how it looked on my new (used) Haulmark,
especially since I live close to salt water. I just finished taking a wire wheel to all the supports and followed
up with a couple of coats of POR-15 rust inhibitor.

[notoriouskelly]

"Planning to do anything with the rust on those supports?"

Let's not get Crazy...

I'm too lazy for that; I'll just cover em up.