Late 60's and at least the early 70's Chevy's (such as the Chevelle's and Impala's) had the fuel filler behind the license plate. As long as you had a good gas cap on them, they would not leak.

You might even be able to find a gas filler neck that has a baffle in it to keep the fuel from sloshing up the neck so bad. Might have to be something aftermarket though.