Hi Jim,
I have a 1989 P27 with a similar problem. I was taking a lot of stuff out for refurbishment anyway and decided to remove the fuel tank. I didn't know at the time that it had a leak. (There was a slight diesel smell in the boat, but I assumed it was the bilge or the engine.) Like you, I searched every which way to get the tank out and found that it was installed before the aft berth bulkhead. The bulkhead cannot be removed in one piece to get at the tank. (Very bad engineering!!) I made a vertical cut, 57" forward of the aft edge of the bulkhead. The panel is 21-1/2" wide at that point. You can cut the panel almost all the way down but need to use a Dremel or Multimaster at the lower edge so you don't cut the fiberglass liner. With the bulkhead out, the tank removes easily. I found that in the original installation, Pearson used polyester straps on the top to hold the tank in place. The polyester straps retain moisture between the strap and the tank and that is where the corrosion takes place. I found 2 pinholes at the edges under the straps while the rest of the tank was like new. I cleaned it out and had a welder spot repair the corroded areas. The tank came out like new again without a huge expense. When I reinstalled the tank, I first used the opportunity to paint the bilge underneath and clean the plastic pads that the tank rests on. Then, I installed some .031" x 1" Low Density Poly strips under the polyester webbing straps, to prevent moisture from accumulating and corroding again. I am about to put the bulkhead back in and will cover the seam with a 1/2" x 1-1/2" x 21-1/2" teak batten on one side and a 3/4" x 1-1/2" x 21-1/2" piece of white trim on the other. I will screw from the stateroom side with oval head screws to make the sandwich. I am really glad that I took the tank out and now with the bulkhead seam, I could do it again very easily. I cannot imagine what someone would do if they were stuck somewhere with the boat and no tools when the tank had to be removed with the stock setup.
Bruce