I, do mostly in part to my driving "style"
would back into every tree within a 3 mile radius while on the trail with that.
Not being DOM material, that may have a little higher likelihood of getting dinged, but should be ok for on road travels. I would highly recommend you reinforce whatever connection your going to make with the tub. The thin 1/8" thick corners you have on there won't be enough. You'll want to drill through the tub and put backing plates on whatever attachment you decide to use. That design with the tire laying more flat increases the pressure on those mounts significantly. Just don't want you running down the road losing that expensive spare and sparks flying. Even though it would make a great insurance commercial....not so good in real life...
Cheers to you for taking initiative to start building your own stuff....I commend you sir.