I haven't scored well in winter yet myself, but my research and advice from the experts is that the sandies will still be around in good numbers in winter - but in the deeper water (14- 25m).
Where I have had trouble so far is that in the deeper water my pots are being dragged by the current. I'm going to have to upgrade pots to the crab'n gear type that is larger and much heavier before I try again.
Get on to Craigie - he has lots of good advice about winter crabbing.
Cheers