Propane supply to B-B-Q from RV propane tank.

I have to disagree with the "only one regulator can be used" crowd. A gas regulator simply decreases pressure if the pressure coming to it is over the regulators setting. IOW, if there is 10 inches of pressure coming at a regulator that is set for 6 inches, it will pass just the 6 inches. If just 6 inches of pressure coming to a regulator that is set for 6 inches, that regulator will do nothing. It will not decrease the pressure.

I put a 10' extension hose on my TT's propane port under the rear outside kitchen, ran it to my Weber BabyQ and purged the air out of the hose. Grill runs fine. No mods done to the Weber, no need to remove the regulator on the grill.

Yes only one "regulator" at a time. However the "high to low flame regulator" on some BBQs does not count as a "real regulator" in this regard.

It is only slightly confusing. :(

Moved from Forum Technical Support

If you bought a 10' hose from Weber or Mr Heater.I've found the schrader valve on the end of the hose does not get depressed enough for adequate flow and the grill either doesn't light or only goes to about 350deg. The fix for me was to use a tire valve tool and remove the valve completly from the hose. You can also just unscrew it a half or full turn and it will help with the flow problem.

Install the T after the RV regulator, than do this mod to remove the Regulator on the BabyQ and add a quick connect on the BabyQ. The problem with your 2nd scenario is you are double regulated causing not enough gas flow to the burner.
https://dl.dropboxusercontent.com/u/50969659/weberq.jpg I got the quick connects from my local RV dealer and the other gas fittings and gas tape from Lowes in the Gas Fittings section.