Some of the newer (and costlier) latex paints are nearing the longevity of the current oil based paints. Surface prep and paint quality are the key ingredients. The current oil paints are not as good as they were ten years ago due to the new epa regs, which have forced the manufacturers to improve the latex products. At our museum we recently shifted from oil to latex because of this. We are currently using Pittsburg's professional products at some $25 per gallon for latex. It's not cheap, but this is not a place to skimp.