The LoRA grind turned me off at first, but 200 images later I'm with you on going local.

The "runs too hot" thing is on you, not the box. Every one of those cabinets has hot spots and cold spots, that is just how they work, and the people who get good results are the ones who stick a probe in and learn their unit instead of trusting the dial. You found 92F at the back wall, so now you know to rotate your dough or prop the door a crack. That is a two minute fix, not a reason to dump the thing. A wine fridge would be worse because those cool, they do not heat, and you would be rigging up a heat source and a fan and a controller anyway. Customer support going quiet is annoying, sure, but they cannot fix a temperature spread that is normal for the design. Spend the 20 bucks on a thermometer you trust and adjust around it.

Six hours total sounds about right until you hit that one spot where the filler just keeps disappearing into a crack that goes to China. And yeah, the primer is more of a hope and a prayer than a real fix in my experience. Once that slab moves with the seasons, those hairline cracks are coming back whether you like it or not. Your mileage may vary but I've never seen primer actually stop them.