You might go to Lowe's and pick up a gallon of Olympic PVA primer for about $12.00 dollars as I remember, you can roll it on, spray it on, or brush it on, allow it to cure overnight prior to sanding, just make sure that it is good and dry. I have used it over a fiberglass surface in the past with surprisingly good results, I did my sanding with 3M open coat silica carbide 180 grit sand paper and DA disks found at my automotive paint store, you will not find this kind of sand paper or DA disk in the 3m gold at your local hardware stores. This stuff acts allot like primer surfacer so don't go to crazy on your application of it, do a couple of test on something you don't care about until you become proficient with it.
I must be honest with you though, most all my stuff is prime filled with DuPont high build Euro primer, and yes it is as expensive as hell... $300.00 a gallon kit, but I also use a base coat clear coat system on the Euro primer.
Last edited by sensei; 10-29-2013 at 05:34 PM.