The tires we use are designed specifically for vehicles with heavier loads and carry a manufacturer's warranty of four years.
We use steel belted Grand Ride ST235/75R25, rated at 2540 lbs per tire, 5080 lbs per axle that should provide you with 30,000 miles of service with proper care and maintenance.
You should be checking the tire pressure on all your vehicles once a month at a minimum.
You should take 70% of the weight off the tires when parking it for over a week.
National Retailer: http://www.tredittire.com/%2FGrand-Ride-P321.aspx