After making a PVC/duct tape prototype in the garage I have definitely talked myself out of it. I did not like it at all.
I then thought maybe mounting two of them lengthwise along the frame? Better, but still not quite pleased...
So, time to start hitting up the local salvage yards to see if they have any suitable moped tanks. In the meantime, I will just move on with the rest of the build and use the stock tank until I either come up with something else, or just pony up the $135 for the Imperial Cycles tank, lol.
I really do like the behind-the-seat keg tanks, but I am planning on running with one of Kip Harley's awesome laid-back seat posts, so not much room for junk in the trunk.
Thanks for the input fellas!