I personally wouldn't do #1. While you will increase your chances of getting out of a burning trailer, you still are at significant risk of death if you are lying on the ground underneath it, injured, unable to get out of the way.
I always thought it was #2. Unlatch the bed and lift it up. As you do that, especially if you pull it inwards slightly as you raise it, it should slide downwards at an angle towards the ground, out the back and away from the trailer. I've done it before by accident while working on the trailer.
Yes, you'll already be close to the door already, but if the fridge, water heater, oven, and/or even the furnace are in flames, I'd rather head out the back.
Dave
EDIT: If the Thetford catches on fire, I'm not sure what to do!