Henk has it about right.
The music shop I frequent has an acoustic guitar room where they store and display Taylor, Martin, and other fine instruments and they keep that room at 50%. The paperwork that came with my Taylor recommends 40% - 50%. I would imagine that drums would be a bit more forgiving than that.
I would also say that humidity is the primary thing to monitor. I am sure the drums can handle temperatures that are quite warm as well as quite cold so long as the temperatures stay rather stable. I have a vintage Slingerland Radio King that was apparently stored in an attic for more than 40 years. It was exposed to extreme Chicago cold as well as heat. There are not any problems with the wood.
Performer 22, 12, 13, 16FT
Newport 22, 8, 10, 12, 14FT, 16FT, 6x14SD
Phonic Plus Gloss Black 22, 22, 8, 10, 12, 13, 14, 15,16FT, 18FT
Phonic Plus 508 Hi-tech
Premier XPK 20, 10, 12, 14