We've started by having a treat jar next to the sofa so that when we're watching a movie and there's gunfire/explosions he gets a treat. For some reason he isn't spooked by anything else at all.

I've been following Will Atherton on YouTube but I'll definitely give Leerburg a watch too, they seem to be very similar trainers in terms of methods. Thank you for the advice. We've got a year to get it sorted which I think is achievable.