Is this a sensible way to do it?
Ah yes, it should be radians.
I suggest you read up on e.getBearingRadians() - I think it returns something relative to what your getHeadingRadians() returns. So the absolute bearing from you to your enemy would be getHeadingRadians() + e.getBearingRadians(), which (I think) is what you need to call your turnGunTo function with.
And you don't need to give me a cookie, just work on your bot and provide some more competition =) I might also be procrastinating for my final B.Eng. thesis - it's due in 2 weeks ;-)