Thanks guys.
I'll book this weekend, but seems I have to book my airport transfer separately sadly.
1- KEF > Reykjavik and
2- Reykjavik > BL > KEF
I plan on arriving for around noon and then taking the 2-230pm shuttle to the airport after before coming back.
Hopefully with it being "shoulder" season and earlier in the day it won't be too bad, but only 1 day to find out.
As an aside though, I have a waterproof camera, I'm thinking that it should be ok and not end up getting ruined?