Hi 🙂 I have travelled from Victoria coach station with national express 3 times now! Never had an issue with a luggage - we’ve had two large rucksacks, a tent, two sleeping bags and two large shopper bags with food drinks etc! When you book, I believe you book onto a specific service ? I’ve always got a seat even if it meant me in one seat and my partner a couple of seats away. Hope this helps - have a great festival!