The 22 guide recommended 20sq ft frontal area which limits it to pop up / teardrop styles, I'd recommend searching for motorcycle, pop up, teardrop & tent campers. I've had 3 different types behind my bike & would recommend Bunkhouse or Aspen brands or for a hard floor a Leisure lite or Roll A Home brands . I don't know of anything with a shower that fits the bill (fresh/ grey/ black tanks add weight) but a vintage Boler or Scamp would be close (tanks / axle on the new Scamp add too much weight). I personally don't like traditional pop ups but you might find one with a shower curtain around a tub/ toilet combo try Colman or Jayco.
Keep in mind the "tow guide"
Is the "no compromise" towing recommendation.
By no compromise, I mean, things you can tow at any speed up any grade.
If you compromise speed for example, drive 55 instead of 75, you can tow stuff with more frontal area.
If you compromise grade, for example, stay in mild slopes, you can tow stuff with more weight. Add trailer brakes and trailer brake controller, and the trailer basically stops itself. The truck won't know it's there when braking.
There are many, many options if you are willing to compromise.
Driving 55 mph to gain a stand-up shower may be great for a lot of people.
This is tall. This is heavy. This has trailer brakes. Did fine at 55-60 mph. It's gonna struggle going 65. I'm happy with 55-60.