If the hydraulic system is unable to lift the roof, it can be done with several people. You would then insert the pins into the cylinders. Then one at a time you would wedge a 2x4 in each corner to take the load off the cylinder, which could then be disconnected from the hydraulic line and removed from the camper. While aiming the cylinder into a coffee can, you can squirt the oil out by pushing the piston down. The orings should be available at any tractor dealer or even a decent hardware store, they are cheap, buy spares