It's a bit of a myth that Brooks saddles can't stand the rain although they obviously need a slight bit more care and consideration than a plastic saddle. My Brooks gets soaked regularly. It sits in the rain every time I play 5-a-side football which usually coincides with a rain shower or, like the other week, an absolute sustained hour long torrential downpour. It got pretty soaked on this year's Bryan Chapman 600 Audax (40 hours) and this year's London-Edinburgh-London Audax (115 hours), both of which involved long periods of torrential rain and the bike sitting outside when I was resting.
The little tub of Proofide you get (or can buy afterwards) does two things. It acts as a slight waterproofing agent (in the week after first applying it water will bead off it rather than soaking in) but its main job is to replace the natural oils that leech out when the saddle gets wet. Too much proofide and it becomes too supple and can stretch. If too much of the natural oils are leeched out then it dries and starts to crack. The middle ground is pretty vast though. It's been more than 6 months since I last applied any Proofide and I've done some pretty horrendously wet Audaxes (Elenith, BCM, LEL, various DIY rides) and daily commuting since then.
It gets wet, it's not a problem. If I'm leaving it outside for a prolonged period then I'll try and remember to put a plastic bag on it, but I sometimes forget, and the saddle is still fine.
As for the tensioning bolt, in normal use you shouldn't need to touch it. If you do (because the saddle has gone slack) then you're looking at about a 1/4 of a turn which will be good for 3 months. The bolt on mine loosens off on its own, I have to put in 2 or 3 complete turns every week or so, but that's because I'm too lazy to find some threadlock to stop it undoing.
I perform preventative maintenance on my chain more often than I do my Brooks.
