I'd be surprised if a dealer would take this on without charging you far more than it's worth.
I did a bit of work on my floor...nothing like what you are facing, but...
If the OSB is not rotten, consider adding bracing under the floor. 1 1/2" angle iron added to factory framing members to support that portion of the floor will do wonders! You could even use construction adhesive to laminate a new piece of marine plywood or exterior OSB to the underside of your current OSB, and then support that whole mess with the angle iron bracing.
If the floor is rotten or so deteriorated it must be replaced, well, I think YOU or any decent carpenter could REPAIR the floor by piecing-in a new piece of OSB or marine grade plywood as a patch.
To lift up the vinyl flooring, I used a carpenter's
"razor knife" with fresh blades. I took advantage of the pattern in the flooring to hide the cut. Using a straight edge as a guide (a framing square is good), I cut the vinyl floor on 3 sides in an area LARGER than my intended work area leaving it connected along one side (I'll call the back of the cut), then I gently lifted the vinyl away from the substrate and curled it back out of the way. Slightly lift the edges of the vinyl flooring you did not remove so you can add adhesive under it when you reinstall.
Since you are working around the doorway, you will need to remove the cabinets on either side of the doorway. In a worst case scenario - screws coming in through the outside wall of the camper and covered in fiberglass (VERY UNLIKELY) you might need to cut these screws with a recip saw. More likely, all screws are INSIDE the cabinet and driven into the flooring and wall framing. Decorative end panels on cabinets are probably stapled on and can be removed to simplify access.
Take out the cabinets, "roll back" a large portion of the vinyl flooring, then ... carefully check for water or gas plumbing and wiring in your work area under the floor. Take appropriate measures to protect anything in harm's way.
Gas lines can be disconnected. PEX can be cut and later spliced. 120 volt electric wires can be disconnected at one end or the other (or replaced altogether), and 12-volt wires can be cut and spliced with crimp connectors and wrapped in electrical tape to keep out moisture.
Next, identify steel floor framing upon which the OSB is resting. Locate your cut lines to avoid this framing but follow it closely so you can later add bracing along side the existing steel framing to carry the edge of your new patch. Cut thru your "bad" section a safe distance away from the trailer frame, and remove a chunk of OSB so you can see. Then you will be able to get close to the trailer framing with your recip saw without needing a degree in 3-dimensional geometry.
Cut along the edge of the trailer frame.
Angle iron is cheap and readily available at hardware stores. Use galvanized or stainless bolts or self-tapping sheet metal screws to attach it. If you use bolts, use nylock locking nuts to keep things together. Paint all steel on all sides, cuts, and in holes (spay paint) BEFORE assembly.
Cut out the bad section of flooring. Attach steel angle or high quality pressure treated lumber - steel is preferable - to support your patch, and install the floor patch. Use caulk or construction adhesive to fill and seal the joint between the patch and the remaining OSB flooring. Then use readily available vinyl flooring adhesive to put the vinyl floor back in place. Use a rolling pin to get rid of bubbles in the vinyl and make sure the edges are well attached. Use an appropriate cleaner to remove excess adhesive. LET IT DRY.
Reinstall your cabinets. Dark Minwax stains do wonders to cover up scratches and gouges. Anything that was originally stapled can be reinstalled with
paneling nails. Use slightly larger screws to reinstall the cabinets, and use gorilla glue on the screws to work like a LocTite and keep them from backing out from vibration. If you MUST relocate a screw, triple check that you won't punch through wiring or plumbing in the process. (My rig had a cabinet screw driven into a 120 volt wire, and another driven thru the floor into my fresh tank fill hose.
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That's the job, and now you can see why it would cost an arm and a leg to get a dealer to do it. Your 2011 RV is not going to be covered by a warranty, so you're on the hook for all of it.
I don't envy the job, but it can be done. These things are slammed together in quick and dirty fashion at factories, so you CAN disassemble them and make the repair. Bring your swear jar. You'll need it. Allot 3 full days for the job. I think it will take 2 days, and the 3rd day allow for inevitable setbacks, trips to the hardware store, busted knuckles, and time to beat your head against the wall. But I would not hesitate to tackle this job.