Whites like a basking spot i have found. My WTFs always seem to pile up to get that spot just under the red night light. I only use a 15 watt bulb and temps are usually around 70 degrees at night mid tank and 72 near the top. My room varies during the night and is as low as 68 and then rockets to 75 to 78 as out apartment maintenance dept somehow has the heating system on a timer and no mater how low we set the thermostat it goes on.

As Jen states, room temp has a lot to do with what bulb you will need. You will also have to take into consideration how much your top is vented since that is going to be where you have the most heat loss.
that said, you don't want to close your tank right up since tree frogs should have good ventilation.
Zoo Med actually has a new stick on fan for about 27 bucks now.