We have rats too, but they eat the wiring in lawn mowers, cars, boat, and RV. They have also eaten the rubber tracks on my Dolphin robotic cleaner and all of my lawn furniture cushions.
Honda and Toyota Motor Companies had lawsuits pending against them because the material that covered the wiring was plant based bio-degradable (eco friendly) so rabbits, squirrels, rats, and mice liked to eat it. I bet all wiring is the same, not just Honda wiring. I have not heard about any companies being sued that actually make the wiring. No matter which heater you go with, the soy-based insulation covering the wiring will probably be the same wiring until enough people pitch a fit.
We keep rat traps baited with cat food under the hoods of our cars now. Sometime we catch them. Opened the hood one night and a rabbit was sitting there! Rat and a squirrel were seen on other nights.
So far, we have replaced wiring on a Honda, Chevy Tahoe, Nissan Rogue., and the riding mower. Have not fixed the RV yet since it is old with 22,000 miles and we are selling it as is. Repair guy pulled 3 lbs of dog food out of the Tahoe. Poor rats lost their winter stash!
I wonder if you could wrap the wire in some kind of tape after you replace the wiring. I have heard rats won't eat steel wool. Maybe you could put some around the wires.
We have tried moth balls in socks or bags, peppermint oil, eucalyptus oil, Capsaisin (hot pepper) oil. They holes in the socks. We tried small animal traps and electrical shock traps. (never caught one.) $6,000.00 of wiring repair, and I no longer thought about being humane!
I guess we could get a feral cat but we'd probably get a lazy one!
I would love to find something besides traps. Please post if you find something that works.