MC on front dual receiver would be a lot safer than at end of 48" extension. Also out of the way for rear access.
2 days before you leave though...
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Few ways, with all in the downward rotation, welding may stop pivoting. But you'd want to ensure there in position
to easily slide in rack. Cleaning for welding with them mounted be a pain.
Could add another bolt in close fit holes to the angle/tube. Even thru the flat plate or both sides.
Drilling while mounted again would painful.
Or could utilize existing frame holes on other side and 'pivot' bolt and add a piece of flat bar.
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Lastly maybe remove rear bolt, insert/drive a very tight fitting tube/pipe between tube walls so when bolt reinserted
you can tighten the heck out of it with out tube wall yielding.
If the holes thru tube are considerably larger than bolts, (only way I can see the pivoting action) could increase bolt size.