Glad to hear the maiden flights went well! Hard to advise on 'cowl' without seeing a picture... hint hint ... I have seen thermoplastic used (e.g. most fizzy drinks bottles I think?), it being melted with a hot air gun over a mould or former. Main problem is accuracy, especially at internal corners. A vacuum former machine would be ideal if you know of one to 'borrow' (as found in many UK schools). Not sure where the cowl is situated (underside of wing?) but might need to watch for effects on aerodynamics of course. I had wondered if it could be made to look like what I assume to be intakes that I think I've seen on real spits, or was that the hurricane?