Jed, if you have things melting, it usually indicates a bad connection or too small of a wire size for the amount of current. What gauge wire are you using to and from the fuse holder? Do you have an infrared thermometer to use to check the temperature of your setup while it is running? How about a friend with an infrared camera? They help immensely. Look for bad connections in terminal ends on the cable, too.
You mentioned that your battery bay is hot. That's not good for batteries, inverters, or controllers, so that's yet another issue which can lead up to short lifetimes of your components, so do fix that soon.
If you don't have any of that equipment, put on a pair of nitrile gloves and feel the connections when it's running high amperage. Most should be not much warmer than room temperature. Anything which feels hot usually has a bad connection or is a bad part. Try a circuit breaker in that spot.