Re spare mounting, I'd use longer bolts inserted from the body side, then run about 4 nuts down on each one as a spacer, then 2-3 to hold the spare on. I wouldn't worry too much about the weight on the back door. I've had two people standing on the spare unloading a 20' 4"diam. sch 40 steel pipe off the roof of a gen1 lwb. I was one of them at about 160, and the other guy weighs about 250. You can look up the weight per foot on 4" sch40 on your own...

Not responsible for advice not taken...