Parts for spare tire setup
I purchased a used,5 stud, bumper/ trailer tire mount off Amazon . But the holes did not line up with the wheel holes for E450, however, I found There is a small hole on the wheel between the stud holes, by lining up this hole at the top and using a smaller diameter bolt, I was able to line up two other stud holes at the bottom. I did have to do a lot of fabricating to make the rim fit properly so it did not stick out. I mounted the rim facing inside towards the RV. But you could also mount it the opposite way it just sticks out much further.
I also had to buy longer bolts to clamp the mount onto my bumper. But make sure you buy grade 8 bolts they are automotive bolts and can withstand much more weight and torque.
A few members on the site told me that there have been issues mounting to the rear bumper. They had said that welds on the bumper can break due to the weight of the spare tire and mount. So I took the RV to my fabricator and he suggested a turnbuckle which I also purchased on Amazon. The turnbuckle is bolted into the top of the arm of the mount and attaches to the welded bumper plate which is bolted to the hitch and frame of the RV. This relieves the cantilevered weight of the mount.