Re: College student taking on 2000 Thomas Saf-t Liner
By underlayment, do you mean the Home Depot 5.2mm Lauan?
If so, that stuff is almost bulletproof and very flexible.
I built a 15' pirogue (cajun flat bottom canoe) from that exact stuff - with cloth and epoxy on the outside and epoxy inside.
It's damn near bulletproof and has handled rough use at my hands for ten years now.
I'm a big guy (250#) and that lauan has stood up to me standing in the boat while it was perched on broken concrete.
It looks rough underneath but is totally water tight and still paddles like a dream...
I guess I'm trying to say that, if installed correctly, lauan is VERY durable and is flexible enough to mold to almost any inside curve.
Enjoying your build too - looking great!