I have a dehydrator with a temp. Control that goes from 85 – 145 degrees. I’m not sure what you mean by fermenting the tomato seeds, but have left them with the gel around them although I did take most of it off. Do you mean leave tomato slices out to dry, then take the seeds out?
Most of the seed saving articles I’ve seen concerning tomatoes indicates that you cut the fully ripe (a little beyond what you’d normally pick) and premium (best on plant) tomatoe in half, squeeze the seed-filled goo into a bucket with a little water and let it sit for a few days – 2 or 3 or so. When it’s nice and nasty, put in some more water and stir vigorously. Then let sit for a couple of hours. The goop is supposed to float to the surface and the seeds are supposed to sink. Poor off the goop into your compost or mulch (waste not, want not), take out the tomatoe seeds and spread them out on wax paper to dry. When fully dry, put them in a container and keep in a cool dry and dark place until ready to use. I’m not sure how long they’ll keep – I’ve seen reports from 1 to 10 years… Anyone?