RamblinAnne
First of all I would look for a plumbing leak behind that fiberglass shower stall. Maybe the shower tap water lines? Those lines are always pressurized to the shower taps, even if you don't use them much. Both of your bulging/ separating issues are walls the shower stall backs onto which makes me suspicious. Did you have the sink out to do the flooring?...or maybe the sink plumbing got jostled during the process and is now leaking?....those walls you are showing in your pics are just Luan over light spruce framing members. The wall between the settee and shower might have some plywood in it.
I have owned 2 Bigfoot campers, and a Bigfoot trailer, and have never had any structural issues.
Yes I know, never say never, but I would start looking at the more simple things first.