There was an article many years back (mix or REP,I forget which) that said to
make it inexpensively, fabricate a door from (2)1-1/2 inch high density
fireproof particleboards glued together using piano hinge hung from a steel
frame, and sealed with refrigerator seal. (magnetic)

Probably weighed about 300 Lbs
Richard H. Kuschel
"I canna change the law of physics."-----Scotty