Hi Martin/ Spud, thanks for coming back and the advice.
I now think I will below waterline go for white, varnish the mahogany and use epoxy for inside.
few more questions if I can-
1. suggestions on process for white below the waterline
2. Varnish recommendations, I see quite a few people use International
3. Epoxy inside to seal, do people suggest Z poxy, or can I just use a cheap thinned epoxy to seal inside
Many thanks for any advice