propane issue

Couple nights ago I saw it was going to get chilly so I started up the furnace and got it set for 62 and it kept us warm all night-heard the unit cycle properly. About 5 AM I woke up and realized it was cold in the coach. Inside temp was 55 and outside was 28. Tried to get the furnace to cycle; fan would come on and I could hear the unit trying to ignite but it wouldn't. Checked the tank and I was at half full. Tried to light the cook stove top and oven but they would not stay lit. Put the refrigerator on gas and it worked properly. Plugged the ceramic heater in to keep us warm for the rest of the morning.
Later in the day when the outside temp was up to 44, I tried everything again and everything worked! Furnace fired, cook stove top and oven lit.
This has never happened to me before. Comments? Assistance and/or tips appreciated.