For your heater, I would suggest a 1 ohm 50 watt resistor. That is what I used on my 51 when I converted to 12 volts. The truck part vendors sell them.
It is quite common for the original fuse holder to give some trouble. Often times there is some heat buildup in the holder itself and it keeps blowing fuses. One common solution is to solder in a new fuse holder. That is what someone did on my 38 Master and it works fine.
