Keeps burning up starters?

First thing is I own a motorhome on a Chevrolet p30 chassis. I had put suburban on form since p30 wasn't listed. Okay, I keep burning up my starter. It works fine for about 2 weeks then it will start kick back (like it hits the flex plate but teeth off). Then it will start to engage the turn motor then just slip and spin, and it will just end up shutting off. Also, my ignition switch is also going out but at a lot slower rate 5 starters to 1 switch. Now the switch story, it all started on a cold night in Oregon. This sounds like a movie trailer, lol. Any way the switch had gone out and the battery wire had got hot and melted the plug casing on connecting wires. Got a new switch and everything has been fine for 2 years. Then it just starts acting up. Turn the key off but the engine keeps running for a second but then shuts off slowly. I know this is maybe because of starter issues. Please help because I don't know how many they will replace before they just stop. Lifetime limited warranty! Now on the switch there are 2 batt terminals one battery wire, witch term is the one to use because I can't tell the difference between them.