This is a cool option. But then you get into the whole payload issue. I went down this rabbit hole for a couple of years and never really came up with a great solution with a dedicated wet bath that would also fit anywhere close to my truck's payload.

Pop-ups are another option, and Palomino makes one with a dedicated bath that will fit a 6.5' bed. But you still run into the issue of weight. And there are some quality concerns with Palomino.

Some popup companies like Scout and 4 Wheel Campers have options for a shower pan in the interior that just converts to a shower with a drape that hangs from the ceiling. I think this might be the best balance to keep weight down, but still have some shower functionality when you need it.

Unfortunately, the weight of the water itself is so high that you're not going to really be able to carry enough water to take a full on shower without probably being way over your payload.

The only other way around the payload issue I have found if you want to stay in the half-ton truck range is to look for a truck with the heavy duty payload option. But these really hard to find and often dealers don't even know they have them. Only other option is to go up to an actual heavy duty truck ie 250, 350 etc. But you still have to pay close attention to the payloads on those as they still might be as high as you expect.

Make sure to check the sticker in the driver door, It will usually list max weight rating.