Are you planning on using or selling them anytime soon? Remove the aluminum electrolytics and wash all the boards with soap and water, let dry, and store. No real reason to do the recap until you actually need to use one and after all the prep work soldering a few caps would be easy. I recap my boards as needed and store them in a cool dry place so they don't leak but I don't have more then a couple spare boards around (Mac IIx, IIcx, IIci come to mind).

If it was me I would probably find a better place then a freezing or boiling attic to store the boards. Fluctuating heat and humidity is hell on electronics.