Question to all those that have done major camper rebuilds

The tub of the camper is simply plywood standing on end, the floor screwed in from the perimeter.

The floor isn't rotten, just badly designed by KIT. It's a 1/2" sheet of plywood outer bottom with 1x2s on top making up an 1 1/2" structure with a ~3/4" particle board layer on the top. Particle board doesn't provide much strength to a truss and subsequently, anything past the end of the main 8' section of floor sags when it's used to hold the camper's weight.

When you lift the camper up, the floor straightens back out. Structurally, the floor should be supporting the over hang in addition to the 12' 1x3s that run the length of the camper in the walls.

I'd love to simply build a whole new frame built on a 2x2 size base instead of the 1x frame that the camper was originally built with, but my barn stall is only big enough to fit one camper in, plus getting new aluminum for the nose, roof, front and rear would be insanely expensive with today's metal prices (Camper would end up being wider because of the thicker framing members).

Inside, the only things anchored to the floor are the two cabinets in the dinette, the holding tank that hangs from it on the underside. All of the plumbing rides up on the wings except for the drain in the shower and the line going through the floor to the tank for the toilet (Single holding tank).

My main concern is the camper simply spreading wide once the floor is pulled, I know she'll mostly hold together given how much flexing the tub does right now because the floor isn't really doing anything to give it rigidity anymore.

The front and rear walls are a truss made with a plywood sandwich which gives them far more rigidity than the side walls, which is simply 1/8" thick paneling over a 1x2, 1x3 frame.

I originally thought about sistering the floor, but the placement of the holding tank, which I'm plotting to replace with a newer ABS RV tank and the alignment of the grey water plumbing under the over hanging floor makes it a no go.

If I pulled the 2x3s that run under the edge of the wings, I could probably drop the whole camper tub as one piece, its simply screwed in to the bottom of the 1x3's that run along the bottom edge of the wing walls.

Being a mechanical engineer with a little structural experience, when one of the main rail beams(two 2x2's with some 1/8"/3mm plywood on each side)and much broke on mine I just did the calcs and ended up with two 1-1/2" sq 16 ga steel tubes(side by side not top and bottom) under each side all welded up. I used some cross pieces and then filled the large holes with sheet foam, the put a rubber pad on top. The mistake I made was in trying to repair the rail beam first, I should have let it sit on my steel frame off the truck for a month or two to get resettled, then repair the beams. With only a two month trip this winter to Mexico it did real well.

If rebuilding I would use a TJI/BCI floor joist which comes in 7-1/2", 9.5", 11-7/8" and 14" depths. Properties are strong, straight, and not much more expensive than structural lumber. Almost any real lumber yard has them, not HD or Lowes.

I'd be happy to help.

Whew. Silver does Class A rebuiilds. I suspect that you are interested in redneck engineering.

Check first to make sure that the floor in the overhang is an integral part of the larger tub. In the Avion it is not. It is attached to the frame and the 8 foot section of floor, but that is the reason that it frequently fails.

So the fix is relatively straightforward. (1) Drop the camper onto blocks to support the floor. (2) Find a way to support the upper part of the affected area - and there's lots of ideas of how to do that depending on the configuration. (3) Tear out the rotten section. (4) Replace section.

You are getting into plumbing and holding tanks and toilets. But they come out and go in like anything else.

Can be done on a budget. Best of luck.

....in the factory visits I've done watching the truck camper construction process, all of them build from the tub up (the tub is built, then the under-wings; all cabinets are added just after walls are connected)...hmmm?

...in my mind, a full foot wall framing (or 2x6 x) would probably need to be built just under the wings and as far rear as possible on both sides, and stabilized against collapse; then the camper lowered onto this foot wall.

You need to work up a real 3D CAD model, with the structure, and do fea runs. The problem is: you don't know where the weak parts of the structure are "hidden", let alone what the structure actually is under "the skin" ! Even worse, the camper floor has to be removed.....by someone working under the camper (extremely dangerous). And, the entire guts of the camper (all furniture, fixtures) have to be removed from the inside 1st (they are all attached to the floor on the inside).

Why even pull the floor:

You really need a structural engineer to have a look, and possibly suggest "sistering" some kind of full camper-length beams UNDER the existing floor, then lowering camper onto the beams (the camper weight straightening out the floor), then with some manner of understructure, connecting the new sister beams to the camper with large lag bolts.

Just build another shell:

What about building a new camper from scratch (and gut all the current appliances and jacks and electrical, and install in your newly-built unit?)...the appliances, electricals, cabinetry, shower parts, toilet, kitchen accouterments and windows and door and roof-top vents are the most expensive components. The shell can be built relatively inexpensively (you could probably frame up the new camper in 2 weeks; then rent a sprayer, and coat the entire plywood structure in water-based quick dry spar varnish several times in 1 day, then attach aluminum cladding from your old camper, and buy what you need to finish the skinning)....?

....just thinking allowed...

I remember reading about a Frank Lloyd Wright house (Falling Water) balcony system sagging down into the river below; the fix was to introduce tensioner cables, then tension them to lift the sagged balcony...