i remember seeing somewhere that if you glued styrafoam[sp?] sheeting to the inside of the tank, it will insulate the tank and help to keep it from sweating.

where would i get the styrofoam to glue in the inside of the tank and what size

the best solution is to install an anti sweat valve.

http://www.thisoldhouse.com/toh/article/0,,218961,00.html