Hi
I am pretty confident that your problem is due to one/several of your doors and/or trunk courtesy light wires. The intermitence is due to the fact that the insulation breaks at the hinges and the plus (rd/br I think) and minus wires for the bulbs touch intermittently at first. Eventually they melt and stick together (messy). Everytime you open the offending door/s you ground the minus wire and bam!
First, disconnect all door switches, carefully dress the wires, fuse C should not blow.

Remove the bulbs and look for intermittent or permanent 7 to 12 volts on the minus wires. Note: It is normal to have + DC on the minus wire (through the bulb filament) until the door open and the wire is grounded, so you must remove the bulbs and door switches in order to isolate it from either ground or B+! If there still is voltage on it, there is a short (usually intermittent).

You will then have to remove the door's panels for further inspection of the wires at the hinges. Beware as there may be more than one of them.

One more thing: some people just move on as soon as they fix their problem. Please post your experience to help others as I just did now