This is an uneducated but handy opinion only.
Seems you might be looking for an easier fix than what you know is in store for you.
You will either need to disassemble the bathroom because as you already see one piece is connected to the next peace and the next peace and the next peace and the tub will likely not come out without the dividing wall removed.
Or you will need to take off a portion of the belly pan and get up in there and attach something to the framing. Wood or some metal fastened to the framing joists to give you some temporary support under that tub.
I don't think you can get the tub unfastened enough to lifted it up high enough to slide a piece of plywood in there from inside the bathroom.
Possibly you could get two 1x 3 boards slid into the storage compartment door and make an X under the tub and fasten it at each end somehow. from what I recall on our tradewind the tub had a gap under it and didn't sit fully on the floor. That would give you a cross brace under the tub just in case you hit a hard enough bump.
I wouldn't use the tub for anything but laundry storage until further fixes become available.
Sounds like you're doing your research in order to fix it and use it and in the end you're going to have a beautiful trailer and as David said Tradewinds are some of the favorites.