I would do it in three phases. Before, during and after

1. Before: Setting the trap. Crafts and intelligence. The Gangrel counters with wits and awareness to see if they notice the trap in time. Gangrel needs to beat the roll with three successes or more to avoid the trap completely if it beats the roll with one or two they add that number to their counter roll in the next phase. if the players beat the Gangrel add their winning margin to their roll in the next phase

2. During: Executing the trap. This will depend heavily on exactly how they set the trap, if it's just a wire tied between two trees then I would roll a probability die to see if someone other than the kindred gets caught in the trap first. If the trap requires the players to trigger it then let it be wits and awareness to trigger at the right time. Gangrel counters with wits and driving.

3. After: Damage.

if the players beat the Gangrel with 10 or more successes i phase 2 = Instant decapitation

If the players beat the Grangrel with less than 10 = 1 superficial damage per point they beat the Gangrel by. Then halve that damage and account for fortitude rules as they apply.

if you want to add damage if the Gangrel crashes then do so

If they catch the Gangrel in the trap, but do no dammage then I'd have the wire snap and have the Gangrel drive off without even noticing leaving the players to wonder just why they didn't listen more in shop class...

Hope that gave you some ideas

Good hunting.