A number of reasons, like I already sanded the wood way too thin and just wanted to smooth it out a bit more without sanding the wood anymore. It is a float plane, not worried about fuel at all but water proofing doesn't hurt, it's going electric too. I'm thinking it would soften just like balsarite or lacquer hair spray too.
Yes Gene, the reason for using cheap lacquer is so it softens/melts and holds the covering down better. It's an old trick for used planes with a bit of oil soak.
Deft sanding sealer gasses off about 80% of it's weight, it's one of the reasons I use it for glassing, that and it is so easy to work with. I started glassing the pontoons yesterday. Any weight gain will be almost nothing so I'm not worried about it a lot.
Can't wait to see the plans Gene. More plans means the Ultra Sport gets pushed back even farther!!! I just put two more builds in front of the kit. I can't help myself, just too many cool planesw out there I haven't built yet!!