The bodytube for a L2D will fit the P3D, however there isn't enough juice for it to work(I have both a L2D and a P3D.) The P3D just flashed quickly showing the batteries are going dead. It shouldn't be that hard to make a 4xAA tube if you base it off of the one for the L2D just longer. I do see your point going with a D cell conversion. That would require way too much work adapting the heads and what not.
Too bad I don't have the technical know how to make a tube.