Can anybody give me some insight on why I'm getting allot of rust on the bottom edge of the tailgate Is there any openings I should look for that may be plugged. What could cause the moisture/water to accumulate in that part? The tailgate shuts tight. The weatherstripping is good.
What am I not seeing?

 

My '93 850 sedan has the same along the bottom of the trunk lid (still not visible from outside), as did another '93 I found in the junk yard—that one was nearly showroom perfect, incredibly clean except for that significant rust along the underedge of the trunk lid (and the damage to the right front that got it junked). The trunk compartment likewise was spotless. Mine wasn't maintained that well, but also has no signs of leakage inside the trunk area.

Does water come in through faulty seals around fixtures on the lids? It must be somehow getting inside and settling along that lower edge.

 

Is the rust on the outside or inside of the hatch? One thought is the seal for th plastic piece that houses the handle, lock and the lights. Maybe the wiper arm hole thingly... I'd pop the inside cover off of the hatch and take a look for any issues.

While you're in there, and if the rear cover rattles around (and really - don't they all?!), you might as well install one of the hatch repair kits from FCP. I just fixed mine yesterday and it doesn't rattle anymore.