A "tee" fitting that can supply propane to external devices is easily added and you can do it yourself if you can handle a wrench. Just get the Extend-A-Flow kit, available in most Rv stores or online. The extend-A-Stay kit also works for this and also adds the capability to run the RV itself from an external tank.
I've had this tee on my last two rigs and installed it myself on the current one. However, I generally find that carrying a 10 lb propane tank is more convenient than using the tee. That because you have to run a hose to the tee and I often want the grill or my gas fireplace further away than is conveninet with the standard 10 foot extension hose. Of course, you can couple more hoses together.
A 5 lb or 10 lb propane tank is easy to carry in the RV and easy to move around the campsite wherever desired.