Nice setup.
An idea for that dropped tailgate, make it removable for use as a table top. On the inside you can install a set of folding table legs. They are readily available at Lowes, HD, etc.
To get more space with a top, have you thought of measuring the top rail of the sides and compare it to a camper top for a small pickup? I saved this for an idea like that.
If it was one of those commercial contractor type, the side windows would fold down to access an inner shelf. Put that shelf on rollers and there you go, kitchen.....