It's been a while (2010) since I last tried it - but we got away with 2 boards, bindings and boots in 1 bag quite a few times. Probabkly at least 1 coat "for padding" Try to make sure it's under 23kg. Definitely has to be less than 32kg.
I've never seen a board bag opened at check in - they get weighed, then they're on the manifest. The guy at outsize baggage will x-ray and send it through so long as it's stickered up. (Apllies to most of the northern airporsts we've used.
Aiport Kgs are smaller than the ones you might have at home.
I think it helps if you book a normal bag too and make sure this is significantly underweight - then if all else fails you can just take your board bag as your main bag, for all that it's outsize.
Honestly this is a sensible implementation of the policy - if I ever go to skis I'll be banging two pairs of skis and 2 sets of board in a board bag rather than wasting weigh having to take umpteen separate bags. (bags are surprisingly heavy on their own)
I think if you're going at peak times you might find they're much stricter.
Good luck at Chambery - never managed to get there and back without delays
Oh - take a load of baggage tags - the ones you write your adress on - they were insisting everyone coming home had them last time - but they weren't giving them out until you got to the desk, imagine the queues...