Well after all the hype in February / March I took the plunge
and bought a spare tire gas tank on eBay. It just arrived
today and I LOVE it! It is slightly tapered on one side and
fits PERFECTLY into my 15" SA Rhein Wheels. It has a 9L
capacity which is roughly 2 1/2 gallons). For pics take a
look at the sold item at:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1807364597

If you want one for yourself the guy seems to list them
fairly regularly. I can't say for sure if his 14" tank will
fit stock 14" wheels... I just took the chance that the 15"
version would fit my wheels and it did. I will post a pic
with the tank inside the Rheins on my website when I get my
film developed (no digital camera).

I have no financial interest in these items and although I
can say that my transaction went smoothly I cannot vouch for
the seller personally. Shipping was a BIT on the slow side
three weeks to Canada.

Thanks,
Chris