The Extend a stay connection
I own a 3050 Sunseeker. The "extend a stay" connection that I have connects between the coach tank and the regulator. This unit has two connectors, one for a external tank, and one for the propane grill (small 1 pound tank type connection). The extend a tank is connected between the coach tank and the coach regulator.
With this setup both the onboard tank and the external tank pass through the regulator, so with a set up like this you will have no problem.