View attachment 5401659
Here's how I ran mine.
I put a dedicated 14-50r outside next to my RV trailer (with a 50 amp breaker in the main panel thats only a few ft away just for it), which I also use for welding sometimes..
Chopped the female end off this 50 amp 250v RV cord:
View attachment 5401660
..and wired it right into the 70 amp "load center" box with 2 breaker spots as my sub panel, up inside the RV. The cord has made it through almost 10 seasons now laying outside between the receptacle on a post and the trailer with no problem. Hail, snow, ice, sun.. Still looks new. I can move my trailer anywhere and just unravel the cord and plug in.
Anyway, one of hot leads goes to each breaker for 120v. I used dual breakers, so I have 4 different 120v circuits to work with (2 on each leg), being careful not to overload one side more than the other, etc. Like the OP, I don't need anywhere near the full 50a for the grow, but sometimes I do run extra tools on the side and whatnot.
I did not use the bonding screw to connect the neutral and ground bus bar.