Since I started this thread, I guess it's about time I replied. In simplest terms, I have learned a lot in the last year.
I bought a JK in May '08, and began trying to figure out how to carry extra gas and water. From my experience in Africa in the '60s, I knew that the Wedco type of cans were the way I wanted to go -- but where to carry them?
Two VERY vigorous outings, one on the Owyhee rim [OR], and another on an extensive trip in the SW, gave me confidence that gas could be safely carried inside. Then we drove 7500 miles thru Central America, from AZ to Panama, this past winter [Jan-Apr], with gas and water inside in Wedco cans with no spillage, no fumes. We used the factory tie down loops in the back of our '08 Rubi 4-dr to secure the three cans with two ratchet straps - one thru the handles [sides] and on on the top. No hassles, no problems, comfortable that we had extra when we needed it.
This was a great solution!!
John