I simply used a motorized auto antenna connected to an eye hook screwed in the upper section of the door. It raises & lowers the door just fine, plus it holds the door closed, preventing predators from lifting it to get in.
I'm planning to use the 5 gal buckets (i.e. from Lowes or Home Depot) with the lids you can buy from here:
http://fowlstuff.com/Stuff.html
They also sell the entire nest box setup if you prefer one-stop shopping.