I have tried this in the past, if you go with using a larger propane tank and running whatever adapters you need to hook up to your grill you should be fine.
Here lies the problem, if you get the appropriate adapters and hook into your RV-Q hookup on your coach then you will have an issue. The RV-Q's are designed to run on the low-pressure gas from that outlet.
This issue is that the regulator that your coach propane bottles run through are rated at a much LOWER pressure than what your coleman or other grill requires to operate. I tried hooking up to a couple different grills and outdoor stoves and neither would run properly on the low pressure output from the on-board gas.
Just my opinion, feel free to bash away, I got thick skin.
Gregg