Hi JohnG just goes to show what a varied life we live. 17 years ago I bought a van with onboard tank wwhich did not have easy clean and in which the pump would not self prime and it has probably soured me for life !
This prejudice has been reinforced by a friends new van with obt which is a complete pain to fill, needing access to pump and valves under seats and waiting to hear the water overflowing to know when full. Also mounted right up front, so no realchoice but to drain down before towing - not very social to next occupant of pitch.
However, I can see the benefits particularly in transit and if installed in a balance neutral position (although doesn't help the all up weight).
Thanks for your contributions and links - I expect my fellow Mods check them out as I do (just in case !!) but increasing the general store of knowledge and experience is on of the major reasons for the forum. Please keep the contributions coming ! Happy New Year from a very chilly
Almeria. Ray