For the "Home Trax" (I like that name) with golf cart wheels and tires.

The common golf wheel is the right diameter for a piece of 2 1/2" thin wall electrical conduit, attached to the wheels with a 2 1/2" conduit connector. On the outside of wheels fabricate a flat plate or use a 3 1/2" to 2 1/2" reducing washer for a nice flat surface for the connector locknut. Set the wheel/tire with connectors between the hulls to gauge length of cut 2 1/2" conduit (measure twice, cut once). Slide a 2" schedule 40 PVC conduit inside the 2 1/2" conduit. Pin through the PVC on both ends with bolt, or other method, to hold in place. Here's a rolling chassis ready for cradles clamped to the PVC. We've seen used golfcart wheels and tires from $8 each with rusty wheels and 50% tread. The kid's old outdoor toys seems to be the "hot" source of cradle material.