and since the engine is in the back and the dash heater radiator is in the front, there are two 30' hoses running to the front of the coach - this hearter radiator is also the high point in the system. It is common practice to instal a needle valve in the top radiator feed hose as a "bleed" valve - the trick is to also install a small diameter hose off the bleeder that you can submerge in a jar of antifreeze. One then starts the engine, brings it up to temp. and then bleeds the air that migrates to the high point in the system and out the valve. The jar of antifreeze may or may not be needed depending on your system.

I intend to install the same type of system on my boat and will pretty much do the same thing. Instead of tapping the nylon fitting I would just insert a needle valve T in the upper most hose. In any case, what you propose is quite commonly done in the motorhome industry.