Need help stretching a chassis

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Need help stretching a chassis

Postby Johnm » Mon Apr 02, 2018 9:59 pm

I presently have two builds planned. The first is a Ken-skill style teardrop and the second is a canned ham trailer. I have the frame for the teardrop all planned out. It will be 5' 6" wide by 10' not including the tongue. As for the other build, I kind of like the looks of one of the campers in the vintage plans section of this website. It is called: 15' Caravanmechill. I have an image of what it looks like:
15' trailer.jpg
15' trailer.jpg (5.62 KiB) Viewed 534 times

The frame on this trailer is 6'6" wide with a floor length not including the tongue of 130". What I would like to do is stretch the width to 7' and add enough to the length to have a toilet on one side and have a shower on the other side directly across from it. I plan to put these just before the bed. Adding to the width will be simple but where the problem comes in is placement of the axle and the holding tank or tanks if I use more than one. I would like to use one axle but I have not ruled out two yet. Any help or suggestions would be greatly appreciated. Thanks in advance

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Re: Need help stretching a chassis

Postby Aguyfromohio » Tue Apr 03, 2018 9:49 am

I recommend starting with the toilet/holding tank and designing the frame members around that first decision.
Years ago I was on a small team that designed a motor home for Holiday Rambler, and those items turned out to be surprisingly important.

Plumbing lines in RVs need to slope like those in your house, 1/4 inch per foot is ideal. Too flat and they don't flow, too steep and the liquids race away and leave the solids behind.
The vertical dimensions that result are key. In small trailers we don't have much vertical thickness under the floor to work with. In a class A motorhome we had the whole underfloor thickness of about 2 feet from top-of-floor to bottom-of-framerails. Pick the particular toilet and look at the plumbing connection and draw out the side view looking port to starboard and looking front to back. Remember a drain line probably can't pass through a frame rail.

In the RV industry they build the black and grey tanks from sheets of ABS plastic (styrene) using methyl ethyl ketone (MEK, butanone) as welding cement. They vacuum formed the bottom and sides from one big 4 x 8 sheet, and welded on a flat top with MEK, cut holes in and out with hole saws and installed bulkhead fittings. The tank shape and size were adjusted to fit around required frame members and fill the available space.

Do a few iterative cycles of design. Place the toilet, work out plumbing and tank location. Examine frame, then move tank toilet and plumbing as needed. Lather, rinse, repeat.

After you have arrived at a workable solution of a toilet/tank system and frame structure, then finish out the rest of the floor plan.
It worked for us. We were surprised at the limitations on where the toilet could go.
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