I was there last week, and didn't end up using the bike lock. The sites I dove were busy enough with other divers where I didn't think any thief would dare attempt anything. I did do Karpata at about 5:30pm one evening when the site was deserted, and saw a teenaged local on a bike as I came out of the water, but he vanished and nothing in my vehicle had been touched. I did my best to limit leaving anything of value in the truck.
I have an old Ikelite Aquashot 3 housing (originally designed for the old disposable film cameras), and I realized it would work well for holding cash, keys, cert/drivers/credit cards, plus a small tool kit, during my dives. I decided it was more depth trustworthy than one of the Otterbox dry boxes etc., and it didn't leak a drop.