For eight years I carried a PortaPotti in my '85, the smaller (lower)
version. With the bed down (the way I normally travel) it fits out of
sight under the bed extension into the living area, pulls out for use
just fine.  It survived without any problems or spills in a rollover
that totaled the '85, and now resides in the same place in my '90 Westy.
I traded off a Westy made box that it would fit into that came with my
'90 that I was told was standard in the Euro versions of the Westy:
took up to much room even though it provided an additional seat in the
living area.  Also would present a problem removing the PortaPotti when
full for emptying. Gross part coming: I have even used this alongside a
busy highway on one occasion when there was no hope of reaching a rest
stop in time, pulled over onto the shoulder, turned on the 4-ways,
stepped to the rear, etc.  Just like the American Express and the
Bentley, 'Don't leave home without it'.

Loren A. Busch
I know that you believe you understand what you think I said, but I am
not sure that you realize that what you heard is not what I meant.