I saw a similar set up that was fabricated from tube steel and had rubber hoses on the pegs, that the bowyer plugged it into the receiver on the trailer hitch of his truck. THAT was a slick set up. Rock solid.
I thought about having a trailer hitch modified to hold my 2x4 frame set up, but just never got around to it.
You can mount the pegs horizontally on your 30" X 30" frame so you are pushing down that works fine too. I screwed another 2x4 on the edge of my frame at my trailer hitch height one time and wedged it under the hitch on one end to anchor it after seeing that other guys set up. That worked ok too.
Get creative bro!