At the end of the day, have you done any research into WHO would be responsible if the mc fell off YOUR fabricated system ?
I would be interested to know if a certified welder would actually give you a bill and full description of what he did leaving a paper trail aimed at him.
When I asked (2x) welders to weld something on a MV they told me they were not DOT certified welders and would NOT accept the legal responsibility due to criminal investigations by state authorities in fatal auto accidents.
Could YOU be held criminally responsible if that happened ? It might be worth looking into and it will depend on which state you happen to be traveling in at the time.
You need to know before YOU start fabricating a motor vehicle that travels on public highways. Personally, I would be thinking trailer that YOU did not fabricate. It certainly shifts the responsibility away from YOU, doesn't it ?