have a look here, it's this yrs progress report(inc 'whippersnapper')
http://www.allotments4all.co.uk/smf/index.php/topic,49640.msg502293.html#msg502293I grow mine in window-boxes.
seed collection?
same as all tomatoes, squeeze a tomato 'til the pips are in a small glass / bottle / whatever, add a little water, leave to start rotting.
lift off mouldy crust, then put remaining stuff into fine sieve, and rinse under the cold tap 'til clean seeds are all that is left. dry on kitchen paper, label and store / give away.
( the rotting process is best way to avoid Tomato Mosaic Virus being passed on, also Tomato / Potato Blight)
;)