I run 28" ET streets and do not run tubes. what I heard from a lot of racers is that on a tire this small and narrow the tube can cause uneven pressure against the tire (mainly the middle bulges out) and does not give the best contact patch. Plus they weigh more. I do not have the hart to screw my new convo pro's so I am running with out screws for now and they do move some not a lot though maybe a couple of inches a night. what I have read and heard as a trick is to use trim adhesive between the rim and the bead instead of screws and they will not move.
my .02