Thanks everyone for the great replies. I did not know that calcium chloride was so corrosive and must be used in an innertube. Since I don't know if the tires are tubeless, and since there might be a reason to not want the weight all the time, I think the best solution is for me to fab up some wheel weights. When I mount the box blade, which I think weighs about 300 pounds, the tractor gets much better traction. And since it is only a 2 wheel drive the extra rear traction is most important. I have about 300 pounds of lead so I will figure out some good method of mounting a 150 pounds to each wheel.
Thanks,
Eric