I'm in the "business" tire wise and the only solution to your problem is to have them foam filled.If it were me though,I'd buy new R4's to have filled and keep the old one's as spares if I could find extra rims.The deeper tread overal on the R4's plus the fact they don't have such huge voids (which have way less rubber than the lugs) that would allow them to be cut or punctured as easily.
The reason for buying new is so that they won't have possible separations in them that could cause a failure.The foam only replaces the air and the tire is
still susceptible to coming apart,and they won't last forever.So if you're going to spend the big bucks,make sure you spend it wisely.
It will add to the weight about as much as they would if filled with calcium chloride or rim guard.
I have a cure for Hoosier Man's hay field problem too of course,invite someone to hunt off all those horny bucks and the sheds will disapear.:thumbsup: and delicious to eat for sure too mmm :licking:
Al