rjxj wrote:
...how do you fix it? Get rid of it!
Nah, don't have to get rid of it... Read on (long).
The foam doesn't break-down, the flexing of the floor under load causes the composite sandwich to come apart and then the skins and foam move independently of each other (and then you can crumble up the foam with continued use. The strength of the material is from the composite action so that's what you have to restore. If it's out of warranty you can make a reasonable repair! We faced the same issue in our Shamrock (Rockwood sister line) right in front of the front end bunk. I did the repair in my driveway as a capable DIYer.
We had 1 bay width (space between frame-to-floor supports) delaminate across 3.5 feet of width. So, about a 1.5-foot by 3.5-foot area. Obviously, I did not want to disturb the finished interior floor at all. I used 1.5-inch hole saw to cut 3 holes in along the centerline of the repair area on the underside. That is, 9 inches from either frame support with one hole at the center of the delaminated area and one hole at either end (approximately) of the area. I didn't have an enclosed underbelly on that camper, but if you do, you'll need to drop it. I cut through the insect/rodent shield fabric and bottom ply of the composite with the hole saw and immediately stopped when the ply was penetrated – so slow speed and letting the saw work without excessive force. I then removed the centering bit from the arbor and used the hole saw, turning by hand, to cut a core of the insulation out of each hole.
I then cut two pieces of 3/4" cabinet grade birch plywood (because it is more rigid and really flat and what I had on-hand) 16 inches by 48 inches. I screwed two strong backs - couple scraps of oak - to one piece to make it even more rigid because of how it would be used (explanation coming up).
I then put a 48-inch level diagonally across the area of the floor in the camper. Heading under the camper with some blocking and a small bottle jack, I placed the jack on the blocking directly under the center hole. I then extended the bottle jack through the hole till it just touched the luan below the vinyl flooring and then continued to raise it till the level inside teetered on about a 1/2-inch "mound."
Then back under the camper with a large bottle of Gorilla glue (polyurethane glue bonds foam to wood without dissolving the foam), a $9 Harbor Freight-MityVac knockoff hand pump so I could dispose of it when done, and 18" of PVC flex tube from for the hand pump. Through each of the end holes I had cut, I delivered the glue using the pump and tubing as best I could across all of the delaminated area between the luan and foam. When I was done, I took down the bottle jack and put some duct tape over each of the end holes - important so no glue drips out in the clamping stage!
Then, back inside with the piece of plywood without the strong backs and 3 bags of fertilizer (dead weight I had at hand). Place the plywood over the delaminated area and stack on the dead weight as evenly as possible. Now underneath the camper with the other piece of plywood and strong backs facing the ground, set the plywood between the frame support across the delaminated area and then use the jack (I actually used two) to press the plywood against the composite tightly plus a little more to press everything together for bonding. I snugged up the jacks after 15 minutes and then a half-hour to compensate for the glue squeezing. Hence, this is why you need to tape the holes so you don’t bond the plywood accidentally. I left everything clamped till the following weekend. It was in the late spring so day/night temps were ideal.
Following weekend I removed my clamping and tried out the floor - solid! I removed the tape and using a can of adhesive, expanding landscape foam (found in the pond-building supplies of your local landscape supply and some big box stores) I filled the holes and let it expand out of them. Incidentally, the foam is pretty much what the factory uses in sealing underbelly enclosure penetrations and it's black. Once set, I trimmed off the excess flush and then patched the insect/rodent fabric with purpose-specific 4-inch wide seam tape I bought from an RV body/frame shop parts department for $0.85/foot (All-Rite brand material). I bought enough to go completely rail-to-rail, and once applied you wouldn't have known a repair was done!
I decided to add some "suspenders" to my repair and cut two pieces of 1-1/2-inch by 1/8-inch steel angle I had around to span between the frame supports and welded flanges to either end for mounting. Primed and painted them and installed them snug against the underside nice and tight. Owned that camper for two more seasons after the repair and it stayed nice and solid!
