Robert Nichols writes:

.....

desired.

I was thinking more along the lines of a double rail, about 3 inches apart,
with diagonal members welded in. I made something like that out of square
tubing a while back, and it turned out about 10X stronger than it needed
to be.

--
Bob Nichols AT comcast.net I am "RNichols42"

Good point.
As a cantilever beam, highest moment is where structural meets the barge.
So add a "doubler" in that region would "do the trick".