Yeah, your right it looks kinda flimsy.     I built it out of 1/4 wall 3 1/2"X 1 1/2 because they fit in the stake pockets and the upper frame is out of 1 1/2 box tubing and some 1 1/2 angle welded in below it.    Also several cross runners that the 2X12 Decking is screwed too.     I've hauled hundreds of loads off of it,   it does have a little flex though, but most of it is from the trailer.           
         Actually when the helicopter is loaded it is not over 3400 lbs.     Sure is weird the first few times being up there.    The trick is getting the trailer driver to park on relatively level ground.                Would like to own a truck mount some day though but this actually works really well,  and if I do out of town work I can unhook and then have normal wheels to drive around if needed.        Thanks for interest.