OrangePeel,
yep, its the dse circuit.
When I put the regulator IC in, I put it in on the opposite side to normal and did the 'same side soldering'. I also didn't cut the legs on it shorter so the legs could be bent and the metal side of the IC was lying flat, but to the outside - if you solder the IC as the instructions say, the metal side is to the inside.
In my case, I made an old style keyhole type hole in the bottom of the case and used an old pentium style heatsink - I was paranoid of the heat output into a sealed box. The heatsink had a hole drilled in the center of it, and then was glued using silicon to the outside bottom of the case. I then bolted the regulator to the heatsink from the inside, thus the regulator was inside, but the heatsink was external. I almost cut a square hole the size of the heatsink but decided it would be hard to seal.
I got the box from Jaycar, about $50 - It has mounting holes external to the sealed inside so I screwed the box to some painted plywood and used a U-Bolt to hold the ply to the mast.
Try this link
http://www.ralphfowler.com/links/dwl900.html for the power requirements of a 900ap+, I assume the 2000AP would be similar in current draw.
I planned to supply about 6 volts to the regulator, but decided it was a waste of time - I supply 12 volts from an ATX power supply and the regulator gets about 11.4volts - it ouputs 5.14 volts.
I tried running my AP from a dirty (standard plugpack no regulator) 12v power supply and it made a noticable but very quiet buzzing noise - may be the 50Hz supply doing something to it - it appeared to work though.
I hope this helps.....
-John