I bought a set of old rims with tires included. Bought some 3/16" thick steel strap of the desired width and rolled a couple bands that fit the rims. Scrounged up some redi-bolts, threaded shaft, and nuts. Drilled holes in the center wheel disk and mounted the tires. Worked pretty good for a number of years. Then one year, the inside tires started to leak where the disk welded to the rim. Seems the welds had cracked the wheel rim.

Bear in mind that no matter how you clamp the rim to the other, using a band (bolts through the disk or eyebolts or nut extensions on the original bolts), the forces you create that are holding the wheels clamped together, are also trying to push the original rim off the disk. Add in the extra forces generated by supporting weight on an outside dual that has extra leverage, and it stands to reason that it just becomes a matter of when, not if; that the welds will break.