I have managed to successfuly overwinter tropical lily tubers in moist sand stored in the house for two winters now. I have the advantage of an unheated greenhouse that I can use to help them along when they start to re-sprout. I put them in small pots in buckets and put them outside during the day and bring them in at night when the nights are cool. Eventually, though, this gets a bit tiresome and this year when the overnight temps were going to be above 50F, I left them in overnight. I think the water/soil retains some heat anyway. A few weeks ago, I went ahead and potted some up into 1 gal pots and put them in the outdoor tanks. I noticed buds on one Rhonda Kay and the first one bloomed today. I was suprised to see it in bloom. I will also mention that I purchased my tropical lily from Kat who has provided helpful answers to my questions.