James:
Regarding Redmist’s suggestion to use closed-cell polyurethane foam tires, those tires add a bit of weight, and often you are trying to keep the weight down on the load, Slime® sealant is cheap light weight insurance inside your tires, just ask any hardcore ATV rider and they will tell you so.
I happen to be in the process of making a hand cart for hauling waterfowl decoys into fields where taking a truck is not allowed, a axle, hubs, wheels and tires from a completely trashed ATV, two pillow block bearings and some serious thought and welding and I’ll be in business for the next season. – Some Call Me Tim