I find that Stainless steel colanders are much better. Just remove the frame from the colander, and use the mesh around the heater. Then you don't have to worry about plastic to heater.
I was thinking it would be alright; but how do i keep the heater form touching the PVC???? I was thinking my be attach a couple of those suction cup things and have tose keep the heater from touching the pvc...What do you guys think...
PVC should be fine, but remember that putting a gaurd on your heater will mess with the temperature read out. Drill some holes in it to let the heat escape into the water.