Gary, now you have me blushing...
As far as I know, any trailer older than mine would have the two valve HW bypass if it is factory installed. (It is possible that it may have been modified to the newer one valve type of by-pass, but that would have been done by an owner, and not Sunline.)
Also keep in mind that the lower valve on mine is kinda hidden and is a bit harder to turn.
What can happen is that one or both of the valves does not get flipped completely and is only partially open/closed. Working them back and forth a couple of times should loosen them up just enough to be all the way open or closed.
On the roof, it's important to know if you have a rubber roof or metal one. Care and maintenance differs as do the caulks and sealants used.
'12 F250 4x4 Super Duty PowerStroke 6.7 diesel
2011 to present: '11 Cougar 326MKS
1999 to 2011: '99 Sunline T-2453
Amateur Radio kd2iat monitoring 146.52