I wouldn't worry too much about the water evaporating super quickly... Just make sure to use a decent amount of water. Heres a couple pics of my tanks with water on the bottom and a heater in them. I use a 100W for about 12 gallons under the eggcrate in my 40 gallon breeder tank:
And a 20 Gallon High:
Do you like that...
That is really a great way to keep temperature and moisture for the plants..
N. Albomarginata, N. Ampullaria
N. Bellii, N. Bicalcarata, N. Rafflesiana
N. Sanguinea (Orange Pitcher), Cephalotus Follicularis.