I know 16 soon to be 17 great pubs for a Sunday Roast actually great for food lunch or dinner 7 days a week, have look at www.peachpubs.com although I should have said at the beginning that none of them are in Sussex
I've been visiting the Duke of Beaufort again, now they have resumed serving roasts. It's at the top of Islingword Road. Shows football on the big screen too.
The roasts are excellent, but it's still fairly quiet in there. Good traditional pub.
Edit: I see you are talking about the outlying areas. Then it's The Trevor at Glynde for me.