Best Thermometer for plastic

I'm looking for suggestions on reading the temperature on my plastic bucket
fermentors. The fermentation chamber (basement utility room) is turning out to be
warmer in the winter than it was this summer. Probably on accounta the furnace is in the same room.

Sooooo, I'm looking to keep the fermentor in a tub, and using the frozen water bottle technique,
but I wanted to know how everyone checks the temperature of plastic buckets.
I'm not acutally a fan of the rainbow temperature stickers, so I'm wondering if anyone uses a probe type, or what.
Opening the lid every day doesn't seem like a good idea, esp. considering the furnace and all.

Here is my setup. I have a second probe to confirm the first and they are within 0.1°C of each other. I have checked the readings against a floating thermometer in the wort and they are spot on.

http://imageshack.us/a/img715/3341/plasticfantastic001.jpg

If you have the room I strongly suggest getting a small fridge to hold your fermenter and a heat belt to heat it if necessary. Buy a simple cheap controller like the one in the picture - about $20 on eBay. Take total control of temperature.

When it is cold like here in winter i do not use the fridge just the heat belt. When not in fridge I also chuck a cover over the fermenter to help maintain temperature stability. It also keeps light out although I have never had an issue with skunking even when left uncovered as it seems light does not get through the plastic like glass carboys.