You can buy a new door liner and gaskets from a couple of sources:
If you are on the west coast, I'd go with
www.sodajerkworks.comIf you are on the east coast or closer to IL, then I'd go with
www.fun-tronicsllc.comIt is in an oversized package, so cheaper to go with the supplier nearest you.
Insulation and be obtained from your local Home Depot or Lowe's, etc.
The liner is really easy to replace - unscrew the 30+ screws around the perimeter, fit the gasket around the new liner and screw them all back in. It might be easier to lift the door off its' hinges and lay it down on a padded blacket, but can be accomplished with the door still on the machine. Screwing the screws in a criss-cross fashion (kind of like the lugs on the wheel of a car) might make it easier.
If reusing the current gasket, clean it up and soak it with Armor-All prior to installation.
Good Luck!
P.S. Nice looking machine - I love the all red 81A's - Here is my all original one!