I'd definately line the inside with ply wood,including the door.The condinsation and other
by products hanging around on the plastic or fibre
glass is a turn off for me.The ply wood would act
as insulation and what not.Also Do you wipe it down after each use.Just my $0.02 worth.Not trying
to bash your smoker,but just giving you some pointers.Also on cold day's I'd run two burners.
One for smoke and one for heat.Good luck,
STRIKE ZONE