If you got good seeds from someone, (and if you are a GVGO member I'm sure you did) it doesn't matter how big your tomato is you can keep seeds and the genetics will be there.
I was talking to a friend today and he was using the fermentation method to save seeds.
That works okay but there are easier methods.
I use the trisodium phosphate....what!
Sounds pretty fancy but it's pretty common and most people have it. You can buy anyplace that sell paint and it's not expensive.
Mix 1 tbsp. in a cup of warm water.
Scoop all your seeds and put them in. Let them sit for 1 hour and all the gel will be gone off the seeds
Rinse them in cold water
Put them on a paper towel and spread them out to dry them a bit
Spread them out on a paper plate and let them dry for a couple days.
I don't store mine in the freezer but i do put them in there for a week. Somebody told me you should do that so the seeds have been through winter. Is it necessary, I don't know. I do know that it doesn't hurt anything.
I rarely have a seed that doesn't germinate
I think John Butler uses the same process but uses Oxiclean instead of TSP.