I've been running a BFGoodrich Radial T/A All-Season Radial Tire - P155/80R15 83S on a trailer wheel for several years. A trailer hub fits the axle. Coupled with a wheel spacer, the combo clears the shock/coilover. Downside - the tire extends past the rim of the fender and you can't use the the original brake. In the second pic you can see a groove in the tread. A shock broke and dropped the edge of the fender on the tire at speed. This shows how much the tire sticks out.
The bottom cushion just lays in there. The back has a hinge that is riveted to the tub. I've had both of mine recovered. On one I didn't reattach the hinge and it stays in place. Easier to access the trunk that way.