Thanks Dwain.
I don't have the freezer yet. Looked at one today which was pretty nice, locally made model, a Končar.
I figured going in through the door might be better because it seems very unlikely to contain anything inside the door that I can mess up when drilling. I thought if I drilled the hole towards the hinge area in the back it wouldn't really be in the way. Open to any other possibilities, naturally.
I had not previously been thinking about using this for two stage or heat too, but it will be necessary to heat during winter. So, means basically even if I could fit the wire for the probe through the gasket, that I'd still need the wire for the heat belt or whatever I'm going to use. Suppose a regular electrical wire might fit through that gasket too, though. The Ranco's seem to have a 1/4 inch wire. Looks like some of the Johnson Analog units have smaller wires but I can't find exact specs yet, just pictures.