Will this bracket work for mounting the bottle in the spare?
I modified the existing brackets by welding a hinge in the bracket just like the ones shown. But you still have to make 2 brackets for those to mount to. I have the 15# bottle shoe horned in with a bottle opener
Yes you can, either use a piece of 1"x6" wood, cut to fit, mount wood in spare area, then bolt brackets to it,
OR
Use some 1 1/2" strapping, bend it, bolt it and mount brackets.
OR
Use some 1 1/2" strapping, bend it, bolt it and mount brackets.

