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!
I think John Butler uses the same process but uses Oxiclean instead of TSP.