Underside as it is not cosmetic.
I am not a fan of the black water tank. I use portable, very portable.
The stinch you drive around with, the need to always find dump stations, some you have to pay to dump, the mess. It can be a hassle.
I took toilet out first thing, frees up room in shower also. I have 3 and 6 gallon portable toilets that can be dumped much easier - in port-o-lets, in any public toilet, on a farm… but graduated to bucket and trash bag - trash cans are abundant. Also, I dont have to appease a female needs.