Best winterizing results:
Air compressor with hose adapter fitting, regulated to less than 60 PSI.
1. Work from distant to close items.
2. Flush toilet multiple times until you get nothing but air
3. Open cold faucet in restroom until nothing but air (NBA)
4. Open hot faucet in restroom until NBA
5. Open kitchen cold faucet until NBA
6. Open kitchen hot faucet until NBA
7. Raise passenger side of trailer, at least a couple inches above drivers side
8. Drain water tank (Could do any time)
9. Drain water heater using drain on outside of water heater near bottom. Repeat a few times, allowing air pressure to build again.
Repeat this 3 - 4 times, and all your lines should be empty. If additional low point drains were added, these need to be opened along the way, and left open when complete.
Once the water lines are clear, pour a cup or two of RV anti freeze in each drain and into the toiler bowl. This will keep the drains from freezing/breaking. It will also keep smelly's from coming up the pipes. I'd allow some into the holding tanks as well just in case. The presumes you already have well emptied holding tanks.
Please feel free to add to, or provide edits to this list if there is a better way.
In general, keep a heater in the unit, always keeping the trailer inside above the condensing point temperature. Also a couple Dry-z-air type units. This will keep the condensate point higher. Keep all doors, cabinets, fridge
, range open. I like the thermostat option for keeping it the right temperature. A cover for the trailer is a must-have. Much cheaper to cover that repaint or replace the trailer, tires
etc. Cheaper to keep it in good shape than it is to repair.