The last ultra heavy duty I used cost $23 and lasted just 2 hours. My 300 jerked the valve stem completely loose from the tube (and no the tire did not slip on the rim). Granted the tire was a very well worn trials tire that had probably been run flat a time or two in the past but I would never run an ultra heavy duty tube in a trials tire again. I switched to the Tublis system last fall and haven't had a problem since."Bridgestone ultra heavy duty but will be change to the neutech tubliss system soon."
Like he said.....
You could have some real fun and run two tubes. drill an extra hole in the rim, insert the extra tube in and place the other one ontop of that. inflate that one. should u get a flat, just inflate the extra tube.