It's a little over-engineered (=heavy) if you ask me.

Just the frame members you have there are over 220 lbs. Add your decking and the suspension and you've got a trailer that weighs over 500 lbs before you even put a sailbox on it.

I think the wall thickness of Trailex trailer extrusions is less than 1/8", but they've also got the slots in them that increases the moment of interia significantly.