Well, there are screw-together valve stems for truck tires, but I don't think they'd work as you still have to get inside the rim to put the stem through. Amphiman's got a good article on the site here:
http://www.6x6world.com/forums/aatv-...placement.html
I've replaced them pretty much the same way and it works. I hate to think how many old flotation tires were thrown away because of bad valve stems!
Don
Stuck in the seventies- not in the swamp.
(6) Attex, a Hustler, a Super Swamp Fox, (2) Tricarts, (3) Tri-sports, a Sno-co trike, 3 Dunecycles, and a Starcraft! ...so far