I am thinking of trying this
http://www.google.com/products/catalog?hl=en&client=safari&rls=en&q=oil+based+white+primer&gs_sm=e&gs_upl=5635l10272l0l10552l7l7l0l0l0l0l123l703l4.3l7l0&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1024&bih=667&um=1&ie=UTF-8&tbm=shop&cid=16141298467292204961&sa=X&ei=XtwxT9DMBeWisQKgg4nxBg&ved=0CEkQ8wIwBA#ps-sellers
I currently use this
http://www.google.com/products/catalog?hl=en&client=safari&rls=en&q=oil+based+white+primer&gs_sm=e&gs_upl=5635l10272l0l10552l7l7l0l0l0l0l123l703l4.3l7l0&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1024&bih=667&um=1&ie=UTF-8&tbm=shop&cid=16141298467292204961&sa=X&ei=XtwxT9DMBeWisQKgg4nxBg&ved=0CEkQ8wIwBA#ps-sellers
Thinking the primer may be even better for adhesion with the water based paints.