Just where I thought you would find a crack. Yes it is frame/structure flexing and there's no real way to stop the RV from flexing in the future EVEN when patching it correctly so it won't leak and still doesn't look like a eyesore bandaid patch. It's not the crack appearance that's the real long term problem. It's the water intrusion that the crack allows into the wall structure. The issue doesn't stop there as water flows downward and the floor is next and will rot and you'll likely have mold be growing in the insulation and the floor area and under it.
The crack must be sealed and covered! The RV's flexing WILL continue because of the actual way and/or the design of the RV's structure as it's flexing significantly around the RV's wheels. The problem long term is NOT going to go away! However, if there is no damage internally now and the crack is sealed/fixed and you make sure it stays sealed, the RV still make do what you want it for. Your description of the crack issue sure does lower what you should pay for the Schooner though by several thousand dollars! You are buying an RV that has a known, seen, and verified problem and you must decide if you are willing to take a chance. May be a fine choice or you may be left with a rotting RV in a few years. Not likely the RV will just break in the middle unless the beam over the slideout area spanning the opening has broken free and allows a lot of extra bending and flexing and ultimate frame fatigue and then fractures. Then the slide side would be prone to dropping down at the rear of the RV. Not good and not repairable for any reasonable amount of money! It will be scrapped!
In RV's, especially towables, the RV unit will be NO stronger than the frame and suspension that's under it supplying the support and carrying the weight on it going down the roadways with bumps etc.
You have some decisions to make and they are big and none will likely leave you totally happy!
