Since my wife.........and the neighbors.........object to the sound of my 6/1, I've been thinking about using a propane tank also, but with a slightly different setup.
Note: The wife's objections are toned down a bit when we still have lights/t.v. and everyone else doesn't.

My idea is to run the exhaust into the side of the tank, at the top. Then, a second pipe will be located at the top and extend all the way down to the bottom, but about one inch from it. The idea is to have the exhaust enter and begin swirling a bit, as it travels to the bottom where it can begin exiting back up through the other pipe. A rain stack and condensate drain would complete the assembly.
I have no proof that such a setup would be better or fool proof, but it WOULD circulate, cool and let the gasses expand before exiting. Somewhat like the old cyclonic air filters worked. At any rate, it HAS to be better than that "pepper pot" muffler that came with the engine!