Getting hot at a switch is a sure sign of a poor connection. Where there is not enough metal to metal contact to transfer the necessary amp load without creating the "fuse effect" . So, after the first bad switch, did you change out the terminal connectors, or the crimped on leads, to be sure they are not burnt, corroded or bad in general? If the lead wires are bad at the connectors, no amount of new components will fix this. When there are bad connections, amp load will tend to heat up at the bad connection and transfer that to the switch itself, and melt anything near it- Just like a fuse blows when it is overloaded. You don't have a short, just a really bad connector, or connection. May be a simple as putting new ends on your wiring harness, or replacing the wiring harness altogether.
I have seen this many times on Astro van fan blower motor connections at the realy module. Napa sold the wiring harnesses separately because of this inherent issue.