I have used Clamcleat's CL234 cleat (www.clamcleat.com) for three years now to rig both my wife's, my son's, and my HH. Of the three of us I am the heaviest at 205 lbs. When used with 6 mm climbing utility line (replacing the original smaller diameter high strength line) the cleat secures the rope quite adequately in both dry and wet weather. What I like most about these cleats is the quick setup, the easy adjustment, and the rapid teardown. The latter was most important once in a severe windstorm and started me on the search for a better way to secure the hammock than the clumsy knot HH recommends. The teeth of the Niteize cleats are very aggressive and I worry about wear on the rope with continued use.
Genco Marine (www.gencomarine.com) has the CL234 for $7.95. Yeah, its a bit much for an injection molded polycarbonate part but since it's a one time buy and considering its good performance I don't consider it to be too expensive.