It's actually very secure. Heavy guage galvanized steel bolted to the L-brackets and three bolts through with epoxy on the pvc. Yes it is held to the frame by that single u-bolt. I've been meaning to replace them simply because the bolt is stainless and the mounting plate has some surface rust. I would prefer it to all be galvanized and of course, "anything worth engineering is worth over-engineering".

However, it's currently strong enough to support my 225-lbs standing on the hull cradle. I've tested it on all four, so that's almost 2.5 times on each compared to the weight of the boat.