Been my experience, in general, that fuses blow for 2 reasons....a short to ground, or too much amperage draw for the rated fuse. Suggest you ensure you have the correct amp fuse installed. Next, check to see if any other electrical "things" (accesories, lights, etc.) have been wired into that circuit that could be overloading the fuse amperage. This is not uncommon at all on used cars, truck and RV's. If that is not the problem, then I would look for a short somewhere on that circuit.
PLEASE let us know how you make out....thanks!
2003 Fleetwood Revolution DP