I'd love to give lightning photography a try, but all I have are the new fangled electronically controlled cameras... they're not rugged enough to be in the middle of a storm.
They say the best way is to chase the lightning into rural areas where there is no ambient light, hold the shutter open (with a remote release) and then close it as soon as you see the flash.
I guess your way is just as good, since it's not wasting expensive film.
