I just got a new TT and noticed a lack of caulking where the plastic shower wall meets the normal wood wall panel. What type of caulk should I use? Thanks.
You can add a strip of plastic / vinyl over the gap to act as an umbrella / roof / watershed which would allow the space to breathe (if necessary) and movement.
I'd caulk it with 100% silicone and sleep at night. My guess; there's enough breathing going on behind that wall. Have you ever slept in an RV on a cold windy night ?