Progress!
Spent 10 hours welding in 90 deg heat today; drank 4 bottles of water, 1 pepsi, and 3 beers. Hydration is important! Finished up the mechanical portion of the RTT rack, roughed out a front basket for the spare and two Jerry cans, and stretched the tongue by 24".
The RTT rack is pinned in the down position like this:
Pull the pins, raise it to the up position, and put the pins in the other set of holes, locking the front legs vertical. It's actual very stable when locked up like this - I crawled all over the top of it and think it will be fine without any diagonal bracing.
With the tent rack raised, it is easy to open the tonneau cover and access the trailer contents from either side.
Still to come are gas struts to lift the tonneau, some form of lift assist for the tent rack (struts, springs, skyhooks, whatever?), and stabilizer jacks on all four corners. After this, it'll be time for paint and wiring! I have to pull the box off again and paint the frame, then strip/coat the interior of the bed before painting the exterior. It'll probably get a few test trips on it before the final paint job in case I need to make some mods.
And now, it's beer-thirty!