Here are some pic's. The frist one is the back corner see how the cover comes from the side and wraps around the back.
The next is the front, see how the cover comes from the front of the truck and wraps around to the side. This is so the air moving across the cove keeps it down. If you put it the over way the air will get under the flap and try to pull it a part.
When I was a helicopter mechanic in the army we had to put bolts in so the air flow would "push" the bolt in if the nut fell off
Had an inspetor get on to me one day for having a bolt in the wrong way (it was on a part that truned) so I truned the part 180deg and said here I fixed it.
Crap this computer will not read my card from the camer how I clear with out the pic's
edit
*Yep thats on right*