Well I just looked in the trunk of a friends MC and saw the panel that mine absolutely doesn't have. Looks like I'm dropping the tank today...

 

Assuming you are looking at the right spot, as it sounds you are on top of this, seems a production issue (monday or disgruntled / union employee issue and im just taking a wag there....) Doesnt matter if thats where you are.

Either way, if the engineered design was to access the fuel pump there, you can cut out the panel and work out some tabs to reinstall it with sheet metal screws or something similar. Sounds like some extra fab work, but if thats the engineered access to replace the fuel pump or similar work in that spot you can do what is needed to access that spot or drop the tank like you said to get there.

Your tech skill level will dictate the course of action. Have you diagnosed fuel pressure at the rail and any electrical or relay problems before convicting the fuel pump?

If I had to do this I would cut the panel out with a cut off wheel or similar and weld up the tabs away from the tank, and now I'll have to look at mine just to see, because i don't like a box of chocolates... But then again, having not looked at it I dont know if i want to throw grind spit down there or if there is room to insert some barrier or insulation beforehand....

 

Sorry man. You must have a strange one off issue. I even confirmed in the shop book for your car that you are supposed to have that access hatch.

Hopefully dropping the tank goes OK. I just did that not too long ago on a '00 Grand Am as those don't have an access hatch). That at least went pretty well.

 

Mine doesn't have one either. 2005 Monte Carlo LT. Mine looked exactly like yours. Anyway, I (carefully) drilled some holes around the ring, then used tin snips to cut it out. I did this today. When I put it back on, I might just cut some sheet metal and get some weather stripping, then epoxy it back down. Welding or using a cutoff wheel is NOT smart and can kill you. Dropping the tank is a pain in the @ss because it weighs a lot, and more importantly, you might rip the harnesses, and/or fuel lines in the process. Better off doing what I did.
PS- Found out my car was in a rear end collision prior to my owning it at 18,300 miles. When the auto body shop replaced the trunk, they probably got the replacement WITHOUT the access panel.