All of the above does also apply to home-built trailers. I own an all
Aluminum Schreder-type trailer, which was built very well. A few years
ago, I inspected the tow bar, which was a 2" square steel tubing. I
took a ball-peen hammer and could easily bash in the walls in several
spots! The walls were very thin to begin with but had corroded from
the inside outwards.
I replaced the tow bar with a 2" stainless steel tube with a slightly
thicker wall. The added weight was neglible. I also ran a loop of
stainless steel cable through the inside around the bolts connecting
the tow bar to the trailer and those connecting the coupler to the
bar. Should the tow bar break, there is still the cable inside, which
will keep the trailer from completely getting away and wandering off
into the oncoming traffic.

Safe flying and trailering

U. Neumann