I modified our old Coleman Roadtrip grill to connect directly to the low pressure propane system and have also done it to our current Weber Q.
Below are photos of what I did on the Coleman. Two regulators in series will not work so you need to remove the one on the grill. Unscrew the knurled/grooved piece from the chrome pipe. Be careful because there is a little ball bearing and spring inside that is a check valve and you should re-install it. On our Coleman, the knurled piece was so tight I had to take it to a machine shop but most find it comes off easily. Keep the regulator in case you ever decide to sell the grill in the future.
I recommend a larger dia. 3/8" hose for better flow instead of the usual 1/4" dia. Also, the propane hoses are available with either a very stiff hose or a very flexible one. Get the flexible one and 20-25' long. Our hose jacket is marked "Gas-Flow by Fairview". Not sure what the technical designation is but I would guess the flexible one is rubber and the stiff one is thermoplastic.
The male quick connect fitting is for propane only and not air and has a different profile. I've been told they are specific to RVs but not positive. I think it has a 1/4" male threaded end. You need an adapter from the hose to knurled part - one end is a standard male flare fitting to match the hose (3/8"?) and the other end is a male fine pitch (1/8"?). I eventually ended up installing a 90 degree elbow at the trailer to reduce stress on the hose.
Use PTFE tape or pipe dope (on thread to thread only and not on flare to flare). If not familiar with propane fittings, you might want to use to soapy water to check for leaks. I went to an RV parts supplier and to a couple of hardware stores to get everything that was needed. Ace Hardware seems to have a good selection of propane fittings. Hoses aren't cheap and will be around $50-100.
