I'm with Jack on this. If your doing a 4' wide build theres only so much room to do things with.
I put everything on the picnic table.
Another thing to consider. No matter how well you take care of a potable water tank, after a while its gonna get Funky! And you'll have to carry a drinking water container anyway.
I put one in one of my trailers and I never used it, it took up counter space and just plain was in the way and wasn't worth it.
Why crowd yourself, you've got the Great Outdoors for space.
Plan for one, use the trailer but don't put it in unless you absolutely can't live without it.
Once its cut in...its in.
Happy Trails
Len