I should probably defer to the more experienced salties here, but what the heck.
This time of year I don't think a lack of heater will be the most important factor--you could probably put the rock in a bucket in either a back room, porch or even outside without much harm as long as it's above freezing. The "live" in live rock is primarily bacteria and it is extremely tenacious. Leave the lid off so there can be oxygen exchange at the surface; if you want to be extra diligent put an airstone on the bottom and the rock on top of that and keep some circulation going.
Definitely take some pictures though before you tear the tank down, it will do wonders for advertising purposes. Are you planning to sell just locally or would you be willing to ship? There have been several people comment lately that it's hard to get live rock orders from the commercial companies that are SMALL enough for the buyers' needs. Nano tanks are increasingly popular and many people would like to get just 2-5 lb or so of live rock to seed the cheap rock underneath. You would be in a perfect position to serve this market and make more money than you would selling the whole lot at once.