I always like to have a functional spare tire.  I also carry fix a flat, a tire repair kit, and a small harbor freight 12 volt compressor (all this, and more, fits in the handy storage area in the very back of the wagon).  When I go off-road in the deserts sometimes I'm 30 miles from the pavement and one spare is a minimum requirement, although on most trips I've never had a flat.  Now and when I get larger tires on my wagon I'll need to carry two spares also depending on the
destination.  If I owned a Brat for desert traveling I would be planning on bringing two spares one way or another also.  Would it be possible to fit two spares (side by side or pancaked on top of each other) on a custom, welded-tube, swing out type rear tailgate on a Brat?  Good luck on your project!

Some SUVs with the tire on the back are easily totalled in a minor collision because you're now destroying your rear tailgate, etc rather than just the bumper.  Something to keep in mind when building it at least.

That's what I was talking about - more damage in minor accident than if contact was made at the bumpers. Sorry for being ambiguous.