Really traditional paint is made of linseed oil and pigment. On bare
wood you first put on a coat of linseed oil then three coats of paint.
All the same stuff - no primer and undercoat. Buy Sweedish Allback
linseed paint from Holkham Paints (Their website has lots of good
information: http://www.holkham.co.uk/linseedpaints/why.html ) It's
expensive but the manufacturers say you won't need to add another coat
for 14 years. Which makes it very cheap. Plus it's genuinely
breathable so the wood can dry out. Modern paint cracks, lets water in
and traps it leading to rot and flaked paint.

"The most expensive paint is cheap paint"