Water damage under floor on current TT 2008 Starcraft

Last Saturday was a sad day. My suspicions regarding soft spots in the black membrane turned out to be worse than I expected. Water had gotten between the membrane and luan and had been in the framing lumber for what looks like at least several years, since one 2x6 was very rotten. It took a few of days to replace what I could get to and put it all back together. Of course some was not possible to get to since it was past the frame. Worst areas were both back corners and forward to the wheel wells. Now I was surprised since I am always checking caulking everywhere and use a winter cover during the off season. We are thinking of looking for a new unit in the off season. My question is do any moderately priced TT's have a better design to keep water from getting into the floor/membrane rather than depending on a bead of caulking and trim? Again my current TT is a 24RQB 2008 StarCraft Antiqua which admittedly is not top of the line, but at the time was best we could afford. All advice is appreciated.