Thanks Steve that's brilliant news as this is my first go with pre peg once I've made the mold but i'm going to take my time and try my best to do it right the first time hopefully .

Hi
You should be able to get away with one split. My, not dissimilar, air duct was made with a single split along the narrow edge.

Alan here from sunny Barnsley lol
I'm making a mould for a air intake to the air box on my Ford Focus RS its an odd shape and hopefully you could help me decide how many splits on the mould I would need ?
I need to sand down the joints then cover with filler before flatting then I plan to spray it to get a really good finish