Progress is slow going. 'Been in a funk the past couple months. I know the cause for the most part and am trying to find a way out. Just takes time. But every once in a while I break through and muster up some effort.
Watching prices fall. BCX 1/4" price locally has now fallen to less than half that of ACX. Down near where I think it probably was pre-hike. Really tempting to throw a load of that in the truck, we'll see.
I decided to go forward with the under-floor spare tire mount. Though, I ran into some issues getting measurements right...
I tried to just make measurements, mark from there, and drill holes.. then have a helper to flip the floor back over afterwards, but too much error stacked up and ended up way off. I have less than 1/4" total clearance between both cross members and the tire. I knew better than to try it the way I did, but I tried anyway in hopes to avoid a bunch of scrambling under the trailer in the dirt.... The holes were for 1/2" bolts, so some 1/2" dowel rod hammered in perfectly with glue lubricating them. Then trim with an undercut saw, leaving minimal sanding needed to get it flush.

Second time around I reluctantly moved on to directly marking the bolt location by using some blocks to hold the wheel up to the under side of the floor. Last minute I decided to mount the tire centered instead of offsetting. I just poked the bolt up through the lug hole and, once satisfied the bolt was perpendicular to the floor, popped it with a hammer to dent the plywood. Followed up by drilling them out from underneath (which is always fun). I used a guide block drilled with a drill press to be reasonably sure I was drilling straight.

I should also mention I found out about torque washers. They sort of convert carriage bolts into flanged elevator bolts, which really simplified things instead of cutting a backing plate and shaping square holes in it to prevent the bolts from spinning. I Like simple!

There will be washers and doubled up nuts against the floor to lock the bolts in place. Also planning to double up the nuts holding the wheel on.