Should I use foam or mohair roller antifouling grp hull?

Usually you would use either a lambswool or medium pile mohair roller. Foam rollers are only for Topcoats generally, or maybe the very thin film racing antifouling such as VC17m or VC Offshore by International. Worth having a couple of types of roller with you, and see which works the best accoring to the smoothness or roughness of your hull.