I had trouble rigging my roof deck, trying to keep it low. Height was a concern as I have a couple multi-level parking garages in my usual routine. And the Sub has enough crown in its roof side to side and fore-aft that there really wasn't a lot of room left in the middle. I went with flat straps as crossbracing and that's a mistake for any real loads, but I was mostly interested in making a flat second roof skin to keep the sun off the vehicle.
My Mk1 idea was to make the deck in two long halves with a lot of handholds / tie-down points so they could be removed and used as backboards.
Mk2 omitted the handhold holes and extended the nose, working to eliminate wind noise.
I hope soon to make a set of 3/4" square tubing cross braces for greater rigidity / strength. But figure I will some day invert the brackets and go to a 3/16" aluminum skin / deck that's flush-mounted with the top of the Z-71 rack rails. Creates a bigger air gap underneath. And I'm really not putting much of anything on the roof. Working on roof-mounting a portable folding solar panel ground kit right now. But having a laser scan / CAD resource for designing such decks would be really helpful. I was using brown paper and newsprint to work out the curves and fit when I did my deck. 'Old skool' pain in the butt.
eta that's 'Mk1' above and this is MkII and the panel mounting frame in progress.
I hope to finish the mounting frame this weekend and get the panel and some temp wiring up there.
A suggesting for your aluminum plank design - maybe work in some slotted extrusions at the outer edges or midline which could fit some sliding / locking tie-down anchors