I took my spare tire off the tailgate this weekend and plan on keeping the spare in the trunk. It takes up too much trunk space laying down so i tried to strap it over the top with the tire vertical and to the side but it was not as secure as I would like and kinda noisy.
What i was thinking was Something like the Rock Hard 4x4 Roll Bar Collars with a tube coming off of it and a spare tire mounting plate welded to that. This would keep the tire off the floor of the trunk and off to the side making more trunk space. I wouldn't be able to use the small section of the back seats which I'm okay with as both seats are usually down anyway.

The question is:
Would the roll cage and/or roll cage collar be strong enough to hold a 90 pound wheel/tire suspended off the floor?
The collars are the same ones used in the roll cage add-ons they sell that are supposed to help in a roll over so they should be pretty strong but could it handle the constant stress of a tire/rim suspended by it?

-http://www.ruffstuffspecialties.com/catalog/STMP-LG.html
Rock Hard 4x4 Fabrication Collar 2.25 inch ID [RH-1225]
And some tubing square of round probably doesn't matter.

 

I have seen a picture of a set up like that and it looked good. If you use the floor to hold some of the weight you should be good. I had a similar set up a few years back but had to remove my tailgate for it to fit. Only reason i changed was i needed the space so the tire had to go! I say go for it and take pics!
This was the set up i ran


Here is a pic i found that has the collars.

 

I actually came across ones like yours when looking for ideas i think. I would go with that kind of setup if my Jeep wasn't my DD, looks nice.
I think you're right about keeping it on the floor for support. If i end up doing it I will for sure take pictures. Might figure out a tailgate vent cover first but hope to get this started soon.

 

While I personally would rest the tire on the floor for support and to keep the weight down low, theres no reason the cage couldnt support the weight of the tire.

Local guy has his mounted off the cage, but as close to the tailgate as possible.

 

That's a pretty sick rig.
I think I'm going to definitely keep the weight on the floor and mostly just use the mount to keep it from moving around. Mine will have to be off to the side with the tread front to back to maximize space. Right now im trying to decide if i want to mount the rim to lug nuts or a V/T shape screw(like the one in the pic attached) through the center of the rim. The Lugs would be more secure but the V or T shape bar would be easier to unmount if I needed the extra space or had a flat.

 

Got my tramp stamp. Had a local guy with a plasma cutter make it for me. Used spray on bed liner. Nice and simple