Love our porcelain toilet except for one annoying thing that might be worth thinking about.
I have found it has a bit of a problem that well, ahem, only men would run into (no pun intended). You must be at least 19 yo and male to read on....
There just isn't quite enough distance to the bowl towards the front of the tank when sitting down and your male anatomy sometimes touches the bowl unless you sit far enough back. Not exactly a pleasant sensation, esp. when the bowl is on the cold side... I would expect a lot of "average" (if you know what I mean) male RVers could find this. I'm not sure what brand/model we have. Don't know if there is a thicker toilet seat available to help overcome this as I haven't looked around yet.
JMHO, but I would suggest looking at a number of different porcelain toilets in person to look at bowl dimensions/configuration before committing, especially for a custom build that is going to be your baby.