I finally broke down and replaced the Gen3 electronics with a RAMPS board and after working through some issues, it finally seems to be working.
I usually print in ABS so I also invested in a Prusa PCB heat bed from Ultimachine. There isn’t much information out there on mounting the thing and most of the pictures I saw had people mounting them on a piece of plywood. This is probably perfectly safe but there’s something that bothers me about mounting something designed to get hot on top of something flammable.
I had a piece of 12″ smooth Hardiboard. This is siding material made from cement infused fiber. It’s very flat, very hard and heat resistant. As a test, I held the torch on a scrap for a while to see what the result would be. It scorched the topside but barely penetrated at all.
It’s a little heavier than I’d like, but the combination of the hardiboard and PCB is actually lighter than the old acrylic and removable MDF that I was using before.
The downside is this stuff is damn hard to cut and throws off a lot of dust. I milled a couple pockets for the thermistor and the wires so the bed would lay flat. I also cut a few notches to remove material and lighten it further. It seems to be working well.