Well, I may have an idea for you, but it'd take a better mind than mine to figure out exactly the parts you would need and at what psi.

The way I'd do it would be to figure out the weight of the rear hatch and figure out how many psi two arms would need to hold up the door in it's up position.  Think of the arms as pistons attached to hinges that pop out when the hatch is unlocked and fold back in to lock the rear once you're done.  Something like a fold out screen for car stereos, only on a larger scale.

The major problems I see with this idea is 1) locking the door back when you're done (maybe a dual bar that when turned one way bolts the door closed, but folds into the door when the key is turned the other way so it will open?) and 2) sealing it shut so the weather doesnt' seep in.

I know, it's after 1 am here adn I'll need to think a little more on it.  I'll try to be more specific later on for you.

i understood everything u said LordKnyght.

i'll start making the plans to actually doing this.

thanks