Survival's 20A Diode Test Load

If you are talking about the insulation between the case and the heat sink, I always use mica insulators which shouldn't change at all with heat.

Mica is very hard indeed, and doesn't have any ploblems with melting (heck, that stuff is what they use for fireplace windows).

Nowadays you see the rubbery-type isulating material more often, which is not really re-usable and more of less intended as a fix-and-forget solution. Very annoying when you replace something since it usually leaves residue so you can't simply slap in a new pad etc.

An issue in this design is that it uses fairly long bolts with washers at the end of the fins of the heatsink, not ones mounted flush with the heatsink backplate. This gives more thermal expansion due to the longer bolts, and combined with the insulating material this is not ideal.

It probably will not matter when you run this at a couple of amps, but when going for the absolute maximum it could result in problems after many cycles.

I like the Deans style plugs being used. Good idea!