I do have an actual fuse. I have a power box that has (2) 30amp actual fuses (for two rv hookups) outside of my trailer. My rv is plugged into a connection to one of the fuses. I have a circuit breaker box inside of my trailer. So my setup is: 30 amp fuse outside plugged into rv. Rv has breaker box inside with 6 breakers. One of the breakers is labeled GFCI (labeled by someone else in pen writing, so could be wrong). When I plug my 1500 Watt heater into a 12/3 10ft extension cord into one of the 3 GFCI outlets, and run it on medium (pulling 6-7 amps- I checked it with a multimeter clamp), after a anywhere from 5 mins - 2 hours, the heater will trip the outlet and the power on the entire trailer goes out, and I have to replace the 30 amp fuse outside in the fuse box. I have tried this on two different GFCI outlets with two different heaters, and two different extension cords, which indicates to me that it's something in the circuit. What's weird is that this wasn't a problem until I accidentally overloaded the circuit with additional appliances a few days ago. Then, now only running just the heater and internet on that circuit (which I've been doing for a month or two with no problem), it can't handle. Thoughts?