Local hardware stores should have those fiberglass gaskets. My stove's original gaskets appeared like woven rope. You'll need some kind of securing substance, but the gaskets (alone) provided by Bradley's Hardware (Wolfeboro) fit tightly enough.
To get a longer burn, use large chunks of "unsuitable" rotting wood--or large unseasoned hemlock. Twelve-inch (by 18-inch) rounds will fit through the front door; however, ashes and embers can leak out
so I use the side door--which will clear 7-inch rounds.
Rotting wood used to be called "punk", and would smolder indefinitely. Indigenous-people worldwide had names for those individuals responsible for "keeping the fire".
My woodstove is perhaps twice as big, and a "round" of unseasoned 7-inch hemlock takes all night to dry out and burn--with the air shut down, of course. Plus, it leaves hot coals to ignite the next day's seasoned birch--which quickly pre-heats the seasoned maple to follow.