Collenite liquid Fleetwax, for me, is the longest lasting ... contains Brazilian Carnauba wax.

For molded non-skid fiberglass decks Woody Deck Wax is the best in 'non-slip" http://www.defender.com/product.jsp?path=-1|10918|309314|311451&id=651529

To make 'any' wax last longer on 'anything' use a pH neutral soap ... McGuires, etc. Caustic detergents or any high pH (pH>8) soap will quickly remove wax.
http://www.meguiarsdirect.com/product_detail.do?q=4599