Condensation on tanks occur during hot weather when the tank is emptied and refilled with very cold water. Insulated tanks are a way to minimize this. However, low flow toilets do not empty the tank when flushed in the standard way. The use approximately half of the water in the tank to accomplish the job. This is done at least in part to give a bit more pressure to the flush with the higher water level in the tank. This means that only 1.28 or 1.6 gallons of water is needed to refill the tank, and this relatively small amount of water is likely already tempered by being in the supply pipe plus it is mixed with the water that remained in the tank. Net result is, the water in the tank is not ice cold and therefore is much less likely to cause condensation on the outside of the tank. I realize this is not a direct answer to your question, but is something that you should consider.