I think you can call my method the 'Bugs Bunny' method...
I sit for a day or 2, surfacing to replenish air, etc.. - If there is no action, move on about 50-100Nm and do the same again.
The idea is to find a choke point, even if it means sitting outside a port. the game is not intelligent enough to localise 'danger areas', so one can get away with this. Once you find a good point, 'milk' it for all it's worth.
RR should be here any moment

to discuss his preferred method.
Both have their merits, and most probably a combination of both would be the best deal.