Dunno about the $$, but read his blog, sounds like he broke the bank. The sportsmobile has a 6.0L diesel he spent a lot of money mitigating it's shortcomings.
I would think an indoor shower install could be done very, very inexpensively and professionally like this:
Custom plumbing, drainage system = a pot and a Sham-Wow!
Perhaps someday. I have a large diesel funmover motorhome, we almost always boondock, we're riders. The van is something I bought cheap and so far, the experience is a success. For a shorter trip, couple of riders, it's great. Like to find isolated places to ride, hike from. A 4x4 would be nice, but for what I'm doing, not needed, yet. I'm basically part if a ride, camp crew, but I am pushing some of the guys to learn to camp off the bikes for a night or two. There are scenes so magnificent out there it would be great to wake up there.
Fwiw tje van foto is on the Echo Canyon trail at Death Valley. Not really a great camp site in there, he must have been passing thru to test his rig on the obstacle. Ridden it many times.
Good luck.