I should have noted that we use two sets of wheels and tires. The 19.5" for highway and long distance travel, they will not air down. We learned the hard way 6 years ago when a 19.5" tire came off the wheel on the beach and after remounting, blew out at highway speed. Fortunately, only the tire was ruined, no truck damage. And a set of 16" Nitto Dune Grapplers for over sand travel. A number of TC's hereabouts use the Nitto's regularly for road use.
There have been a few light weight rigs here, that have aired !9.5" tires down without problems. The 19.5" tires do not have a bead, so I think it's risky even with lighter TC's.