I'd never take the hard ones on the river as well. Will boats like that, they must be made of one contious piece of plastic. So, would literally have to be molded at once with ZERO seams to be considered for river running. A welded polyurethane seam will pop under enough impact (which will happen at least once river running).
MMM, if I were you, I'd simply stick with simply air in the tubes. It's your best bet. Plus, the air inside acts like a shock absorber. you will eventually tag a rock, or even hit something under the boat. Will help deflect the blow. With tubes being more solid, not sure what the boat would do at that point hitting something.
"Good angling ethic is not a monopoly practiced just by fly fisherman" - Bill McMillan