I wouldn't routinely carry gas in the trunk. However, if a hurricane was bearing down with an uncertain trajectory and evacuation in the next few days was a distinct possibility, I wouldn't have a problem with temporarily putting some extra gas in the trunk. Assuming of course that I had it in suitable containers.

It is all about balancing risks. I routinely drive around with 10-15 gallons of gas in the tank, which is under the car right below the trunk. There is some small additional risk of having some in plastic jerry cans in the trunk. Balanced against that is the risk that I might really need that gas if I had to get out of Dodge ahead of a storm. When and if the threat of evacuation passed, I would of course empty the jerry cans into the tank as soon as practical.

How one assesses the relative risk of carrying extra gas vs running out during an emergency is of course a personal decision.