Have you seen this thread...
Clicky. We have been talking quite a bit lately and even taking measurements on each others bikes (convienient since we live about 10 miles apart).
I'm not concerned with the COG, 4.8 gallons of fuel will not be nearly as noticable as those PITA passengers squirming around.
I've been following Joe's aux tank projects since he started. I am not a fan of the Tanji style tank and the Bennet tank is too $$$, so that leaves something like Joe's current aluminum tank project, his JAZ cell or the one you guys are working on. Pricing is a big factor and i'm definitely going to use a fuel pump (with the grav feed if it works at all in the lower mounting position as a back up).
Unfortunately i'm afflicted with the "twisties" disease (especially having to spend so much time being exiled in stinking Flori-duh) so i'm unable to go slow when i come to any turn thus i don't want to hinder the bike's cornering dynamics by having that much weight even a few inches higher than necessary.