Removed Ollie's spare tire housing again and firmly pulled across one area of tire tread to see if the spare tire had complete contact against the fiberglass hull. It moved a little, not as easily as @Dirt Duff tire. The wing nut was causing friction against the wheel, I thought the spare tire was tight contacting the fiberglass hull completely with the 225/75R/15 spare tire. Believe the same thing was happening with the original 215/60R/16 spare tire, too. Both tires were contacting the fiberglass hull previously in areas, but not completely.
Cleaned the area on our camper where the spare tire contacts the fiberglass hull and installed four 3 1/4" diameter 1/4" thick door knob pads for the tire to contact like @Hokieman did on his spare tire. With two nuts still on the stud and four 1/4" thick doorknob pads installed on the hull for the spare tire to contact when tightening down the wing nut, the tire contacts all four pads with clearance left between the wingnut and two nuts.
I'm keeping two nuts on the mount stud, but in some cases there could be contact between the second nut and wingnut on other Oliver spare tire installations like it would be on @jd1923 trailer, possibly due to small variations of wing nuts, mounts, wheels and tires.
Really like the plastic disc @Townesw installed for the wingnut to contact when the wingnut is tightened against the wheel.