Hey Swampy I have a personal mix that works wonders and is cheap to make, I used it to do my bottom, fill nicks and reshape the rear of the hulls where it had brokern away from the rudder pins. Here it is:
Fairing Putty: Resin - 3 to 4 parts microspheres - 1 part cabosil
Mix well will turn into a think marine tex looking mixture, apply with squeegy and sand smooth(3 sandings by hand 100 light, 300 light, 600 wet) Give the whole boat a light sand to rough up the gelcoat and have it painted I had both my hulls profesionaly shot with Emron for $200.00. This is the long but proper meathod of doing it, I'm all about looking good as well as sailing fast so this meathod was worth it for me on my 79 boat. Here are a couple more useful mixes:
Glazing Putty: Resin and Cabosil mix to desired texture
Bonding Putty: Resin - 3 to 4 parts microsphere - 1 part milled glass fiber
Good luck
Peter Cherrick
H16 ElDiablo
USA 37848
http://groups.yahoo.com/group/necatsailors