Portawalls..what size/type tire?
When I looked into use of portawalls two years ago, every model that I checked into had a warning not to use them on radial tires -- it wasn't highlighted in the advertising, but was burried deep in the specifications sheets. I never did go ahead with the idea as I didn't want to chance violating manufacturers instructions, and I knew that i didn't want to go back to bias ply tires.
Good luck with your investigation!
Kevin D. Allen
WBCCI (Lifetime Member)/VAC/Free Wheelers #6359
1964 Overlander International/1999 GMC K2500 Suburban (7400 VORTEC/4.11 Differentials)
1978 Argosy Minuet 6.0 Metre/1975 Cadillac Eldorado Convertible (8.2 Liter V8/2.70 Final Drive)