I don't have 5 gallon buckets but you could do them with two of these.
"
http://s697.photobucket.com/user/acebird1/library/Honey%20warmer"
These are styro containers use for transporting drugs. Drug stores fill dumpsters with them so they are free.
The bulb is a 10W LED you can go to a 13W LED an old 15W night light or use multiples.