Clam shell TCs leak at the same place that other TCs leak. That is, they leak around lights, skylights, vents, etc. Once they get wet, they are just as bad as other TCs. Even fiberglass boats can leak around through hulls.
I think it would be possible to build up the low area though, but let's not pretend that clamshell fiberglass campers are perfect. Then, there is the major limitation of clamshells for some of us. That is, they have very limited space inside compared to a TC with slides.
If one design was perfect for everyone, there would be only one. :D
