Is having a broken water line worth the chance that you might be able to take your RV out on one more weekend trip?
Small diameter plastic hoses for water lines, and cheap usually not tightened properly plex fittings, just waiting for a small amount of water to freeze so they can blow apart.
Weather man can predict aboving freezing temps, but we all know that is NOT a guarantee and we all have often seen temps drop below freezing in the middle of the night even though the weather man said it wouldn't. :R
And the repair cost is not just to fix the water lines. It's the huge cost of all what the water will damage.
Leaving heat on will not protect all your water lines.
I use the method of pouring antifreeze in fresh tank and pumping it thru out all the water lines. That way "I" know every inch of the water lines, water pump, toilet are filled with antifreeze.