[KeithInUpstateNY]

I'm guessing the refrigerator is a residential 110V only model from the fact that you said the tech said you could slide it out and plug it into an extension cord. In homes The refrigerator is usually on its own circuit/breaker so that there is less chance of an overload and losing everything in your refrigerator if the breaker trips. Not part of your current problem, but if be cautious about using the pantry outlet. The fireplace heater draws enough power it SHOULD be on it's own circuit. I suspect the burnt 12V slide fuse and the non-working 110V outlets are related. When the slide moves in and out the electric wires have to have enough slack to move with the slide. If the cable feeding the refrigerator, etc wasn't routed properly, or is too short or too long it might have caught on something and been cut and/or disconnected at one end out the other. This would have likely also caused the slide to bind resulting in the burnt fuse. Not a solution, just some insight in case you end up getting a residential electrician as opposed to an RV tech.