Donald Westlake is a natural treasure. His humorous caper novels are legendary, and this is one of the best. The idea here is that instead of robbing a bank by breaking in and removing the money, they'll just steal the whole bank. Temporary banks often reside in mobile home/trailers while the new bank building is under construction. Why not just put the wheels back on and tow the whole bank away? Then you can take your time in getting in and extracting the money.
It should be easy, but things never quite go according to plan in a Westlake caper.
This classic novel was made into a movie, but the book is the right way to experience this misguided attempt at larceny on a grand scale.