Propylene glycol Is available at over the counter at most any drug store. Just ask the pharmacist for a pint. Probably less than 10 bucks and enough to last for years. Mix it 50/50 with distilled water and charge the floral sponge with the mixture. It regulates the humidity to keep it from going above 70%. Once the wood dries a little you shouldn't be getting high rh. Also, it is supposed to help prevent mold. Is your sponge in a preforated container? Good luck