Looks good. Hell of a deal on the cap. I am looking at a similar idea however I have a rooftop tent to mount on top and will be building a rack for over the bed. My debate now is whether or not I want a cap to keep gear dry or use tool boxes.
As far as ideas, you will probably want to make some screens for the windows (unless I just cant see them) due to the Texas heat and black color. No one wants to sleep in a solar oven. [emoji16] Maybe wire up a fan for some air circulation.
I would recommend running heavy cables to the bed for a s-pod or similar device that will have constant power. You can then add lights and other accessories to that for running less wires and for ease in disconnecting. One main plug from the battery will be much easier and the s-pod has all the fuses built in. Make sure you can monitor battery voltage from there too.
An awning (180 or 270 preferably) mounted to a roof rack on the cap would provide shade from the Texas sun as well as rain cover.
Maybe a radio in the back. I like getting out and unplugging but I dont put the radio in that category. Nothing like some tunes around a campfire.
I could keep going. Just rattling off things on my list. [emoji23]