After the acrimonious debate a year ago, I took the advice and joined BALPA. I don't regret it but at the moment BALPA is completely invisible in Jet2. If you go to the BALPA website, Jet2 does not even exist, it's still Channel Express.
I'm not sure that Jet2 does collective negotiation, with crew reps, BALPA, IPA or anybody. Maybe the answer is to take any problems direct to the man who can fix them. In other words, if you don't like dual basing then complain (again if necessary) direct to NH - all 100 of you if necessary. The same could be applied to any problem.