I have never been able to find any safety issues with carrying jerry cans on the inside. I read a lot of posts on this and I am very curious what is an actual scenario that is realistic. Obviously nobody is going to leave the cap open and let it slosh around until you have a river of gas in the back seat, then toss cigarette butts in there one after the other. I heard the static discharge theories and I am not butying them at all. Besides the fumes that may linger immediately after filling or using the jerry can, I cannot think of any other comfort concerns. And if you are rear ended hard enough to set off the gas in the jerry can, by God man you are already twice dead. I would love to hear reasonable safety concerns. I have been carrying jerry cans full, empty, half full, half empty, and I am still alive. If I am convinced it is a safety concern, i will carry it outside, but I can think of many more reasons for the cans being outside as a safety issue.