In the mini series Sherlock the character by the same name referred to his mind as a castle. a castle that he would figuratively travel through. Each room was filled with knowledge that he had stored away for him to easily relocate in a time of need.
A Mind Doublewide is the poor white trash version of that. It is a repository of usless information mainly comprised of Pro Wrestling knowledge, 1980's action movie quotes, blist actor names, ways to work over the government, and dead cats. lots of dead cats.
"how are you able to quote this movie dude? Who has even seen this man!?"
"Didn't have much to do back at the trailer park, buddy. Its all in this Mind Doublewide."