just after some advice on what to prime fibreglass panels with before painting with acrillic paint.
Do you have to spray a fibreglass primer before applying the acrillic primer/undercoat
Also what is the best way to fill/fix the cracks you get in fibreglass guards, will applying a coat of resin fix the problem of them recracking in time or is that only a temp fix
Any help would be muchly appreciated

The same primer as used on steel is fine for fibreglass.

In my experience once fibreglass has cracks in the resin, you will need to re- resin it to fill the cracks and stop them.

If it has cracked once, it may crack again, but not the same cracks, new ones. Stones flicking up from tyres under guards are good for star cracks.

Repair all the cracks with 2 pack nikki or bogg, Key the whole surface with up to 36 grit sand paper preferably on a sanding machine of some type and use a good high build primer surfacer, after that its buisness as usual with your top coat, whether you use single pack or 2 pack the basics are similar