Not a big fan of running the water for many reasons. I can understand in the house as the water is under constant possible need and you cannot easily flush out the house system, but not really practical for an RV / TT.
1) There is of course the environmental impact and why waste the water. After the reports of drought, etc. and we have the trailers to visit nature, I think we should be doing our part to protect what we have.
2) Flushing / blowing out the system is not that big of a deal. (did mine in just a few mins the other night when the temp was at 32 degrees)
3) There is no guarantee it will work. How much do you let it drip vs how fast it will freeze. I looked at my gutter downspout this morning and it was a solid 2 ft icicle. That water was running all night and still managed to freeze. Don't have much faith in a tin can filled with water in the frigid cold.
On a side note, not a big fan of antifreeze either though. No, I'm not Ule Gibbons, but just the idea of adding a foreign substance to a porous plastic system and then later going to put drink from it. If it puts hair on your chest... better check the bottom of your feet too.
Sorry for the sudden soapbox, but man do I feel clean.