[AdamHeard]

If the wood is rigidly attached to the frame along it's length, you could probably get away with no internal cross members.

Also, You appear to be using 6" wheels, which is fne; but I think you could save a substantial amount of weight by going smaller (and keep the same ground clearance by shifting the wheels down).

For season, I'd ditch the adjustable center drop and go with a value you know works, saves some parts and weight.