Is there a way to see what areas are covered by lightning rods already, while placing other rods?

Unfortunately, not for now. But it's possible to improve the mod adding this feature. I see a couple of options:
1. Make rods be subtypes of turrets (similarly to meteor point defences in SE). Simple approach, but leads to confusion.
2. Draw custom semi-transparent circles or lines to visualise defence and attack ranges. Seems better, ah?

Well, it's a good feature request, thanks! I'll try to find time and motivation to develop it.