WARNING - WARNING - WARNING
Do NOT do this unless you are 100% comfortable with what you are doing and know the consequences of fire and death if done incorrectly or with disregard to safety or knowledge.
I did this many years ago in my Ole Toyhouse. (Toyota 21 ft MicroMini) see the link at the end of this post.
I initially tried using an adapter on the Mr Buddy 1 lb bottle connector. I discovered that the MH low pressure propane (11 inches of water) was not enough pressure to push through the Mr Buddy regulator.
The Mr Buddy internal regulator takes the high pressure 1 lb bottle, and regulates it down to 11 inches of water. This is the same as my MH, so I modified my Mr Buddy and put a "T" on its internal low pressure tube (after the internal regulator), and added a connector on the back of the Mr buddy with a quick disconnect.
I could now supply the Mr Buddy low pressure system with low pressure propane, directly from my MH.
I later suspected that I had a very small leak in the Mr Buddy's internal regulator, so I once again tore the Mr Buddy apart and removed the internal regulator and connector that connects to the 1 lb. tank..
The Mr Buddy now operates entirely on the couch low pressure system through a hose that's plumbed into my house propane.
When I modified the coach propane system, I installed a "T" in the propane supply tube near my water heater. I added a ball valve and then a 10 ft long hose with a quick disconnect on the end. The quick disconnect mates to the quick disconnect I have mounted on the back of the Mr Buddy.
When not in use, we disconnect the quick disconnect from the Mr Buddy and also turn the valve off.
If you do this, use only an LP approved Quick disconnect fitting.
How to - Ventless Heater - Improvement and Do-It-Yourself Projects you have done to Share! - Toyota Motorhome Discussion Board
In the above article, I added a "T" inside the Mr Buddy. I have since removed that "T" and the internal regulator and 1 lb bottle fitting. ..