We have been full time for ten plus years over time my wife and I noticed the kitchen floor is bowing/rising long ways with the slide out. The bowing floor is under the linoleum. If you're in the RV and standing in front of the kitchen countertop the bow extends under the water heater into the living room about a foot and gradually decreases towards the right side a couple of feet in front of the kitchen pantry. The rising floor is deforming the paneling that the propane detector is mounted on. Is this frame flex?
Yikes. Did you hit anything on the road? If not, then look for rot under the camper. Usually a rotted frame or floor will sink and therefore make the good part of the frame and floor look like its rising. Hopefully, its just the floor. That's easier to fix than a rusted weak frame. The floor can be fixed by either lifting or jacking up the walls or sides of the camper and putting in a solid thick floor structure.
Hope this helps.