There are loads of places to ride in Brighton, don't just look around the seafront and the level. There's some good walls at Sainsbury's near the train station, and I've seen loads of little spots to ride while just shopping in Brighton and riding about.
Remember, when you're not riding, look at your surroundings and think what you can push yourself to ride on your trials bike, it's what I do and I often end up riding in spots I never would have thought of later on.
I live near Brighton, ever heard of Lewes? If you live nearby we perhaps ride together at some point, I know a couple of locals that would be up for a session.