Not sure if you already have the Foam Inserts, but if you decide to go that route, the foam inserts that Robarts sells are expensive and are made from 'Backer Cord', which you can get from Lowes or Home Depot, look in the Concrete/Masonary Section, you can get a Roll of the stuff and comes in different diameters, the larger diameter the stiffer you make the Tires/Wheels; its also found in the Storm Window/Door products section, where the weather Striping is located, there I think it's called Caulking Cord.