I usually use woven glass cloth. Chopped strand mat is held together with a binding agent which dissolves in polyester resin, but not in epoxy resin, so don't use csm.
You can get useful information from http://www.gurit.com/sp_home.asp?section=000100010022§ionTitle=Marine This firm Gurit, took over SP Systems a few years ago.
I get my materials from www.cfsnet.co.uk who are based not far from me in Cornwall.
Powder bound CSM is available on line from CFS together with all the foams, fillers, tools and information you could possibly need. They also supply degreasers, mould release, acetone etc. in decent quantities. (I have just rebuilt a rudder, all the stuff came from them, they may not be the very cheapest but have comprehensive stocks and carriage was reasonable)