1. Turn off the power, both 120v and 12v
2. Disconnect water source
3. Turn both propane valves off at the tank. Light a stove burner and let it burn till it goes out.
3. Remove the electric box cover then disconnect the three wires from the 120v Romex cable. (the white wire at the blue connector beside the switch) Slide the Romex out of the connector. Put a wire nut on the black wire just in case anyone turns the power on.
4. Disconnect the 12v
wires black (+) and white or green (-) Put a wire nut on the black just in case someone turns the power on.
5. Disconnect both hot and cold water lines where they connect to the water heater.
6. Loosen the brass nut where the propane pipe connects to the water heater.
7. Remove the putty that seals around the copper propane pipe. From beneath the trailer you also will have to remove the putty where the copper pipe penetrates the belly pan and remove the clamp that will be near that penetration. This will allow the copper some flexibility.
8. With your finger push the copper through the water heater cowl and down to the level of the plywood floor. Depending on how your pipe is installed you might have to leave the pipe as it is and work it through the cowl as you remove the water heater (step 12 below)
9. Remove the door then remove the screws from the perimeter flange.
10. CAREFULLY cut the caulk around the perimeter of the flange. I used a utility knife, but any very sharp edge will do.
11. Push a putty knife in between the flange and the trailer skin , everywhere all the way around the perimeter. The adhesive caulk should only be at the perimeter that you can see. The butyl caulk tape behind the flange should release easily.
12. Once the flange is loose, gently lift while pulling aggressively outward. The foam cover should come out through the existing opening. There should be a block of wood beneath the water heater that will allow the water heater to slide out without dragging the bottom.
First time I did this it took me a few hours. I can do it a lot quicker now.