as far as i know, any newer 27' 5th wheel will have an ultralight frame, which attempting to tow a boat with, will void the frame's warranty and possibly the trailer's warranty if any flexing causes issues with the walls/roof.
maybe an older 27' 5th wheel might not be an ultralight but without knowing the year/make/model, can't say for sure.
Dan-Retired California Firefighter/EMT
and Zoe the Wonder Dog(R.I.P.)
2016 PrimeTime TracerAIR 255, pushing a 2014 Ford F150 SCREW XTR 4x4 3.5 Ecoboost w/Max Tow Package