Thanks tijai and Michael.

Michael, where you say join as a solid, do you mean create additional sides so no open planes exist? In the case of my fuselage it is all open.

P.S. Joined the visible surfaces and exported as lwo and it was much better thanks. Some flipping required but was entire sections (e.g. wing, etc) instead of surfaces (e.g. wing top flipped and wing bottom not flipped).

Thanks again

Steve