Well, I found a leak.  I'd like to say the leak, but that remains to be seen.

I would appreciate advice on sealants or such.

The leak is in the seam between the plastic piece the heater hose 
connects to and the body of the heater.  There is no picture of this in 
the Bentley that I have, so I can't refer you to a page.

It's a seam that is perpindicular with the orientation of the camper 
body, if that helps, and seems to be on the top hose connection.  (By 
that, I mean the entire series of pieces that makes up the plumbing 
there.  The hose connection itself and the next joint are tight - this is 
the joint that is at 90 deg to the hose).

It didn't leak till I accidentally nudged it will cleaning up some small 
trace of coolant.  Obviously it had leaked at least a little before.  In 
addition, it would almost certainly permit air back in when the system 
depressurized after cooling off.

 Jim - Farmer - Iowa City, IA, jnmeade@blue.weeg.uiowa.edu