Yeah, you could mount it where the light was. But you would need to rewire it. Don't use the existing wire.
Find yourself an adaptor that meets the requirements of the fan and you are all set.
Make sure you mount it on something so that it is not flush, you will need to have air behind the fan to circulate properly.
I mounted my fan on the bottom to push air up from the heat tape. But I also have a lift top and flexwatt on the floor of the unit only.
-Steven