They always were a cut above the others
I've just had a read of the tin and a quick google on painting fibreglass. On the fibreglass front, acrylics seem to be mentioned quite often so there shouldn't be any problems there. The other thing mentioned was the tendency of fibreglass to absorb moisture which will screw up the paint job nicely - and Anglesey isn't the driest place on the planet.
Re Simoniz Tough Black - minimum spray temp 21 degrees C, so you'll have to wait 'till summertime - which I'm reliably informed will be the afternoon of June the 21st this year

You never know whether the minimum temp takes into account the cooling that takes place when the propellant in the rattle can expands lowering the temp of the can. Whenever I use a rattle can I always warm it up by filling the kitchen sink with hot water and standing the can in it for 10 minutes or so immediately before use. I always wipe the can completely clear of water before using it because drops of water on the work can really spoil your day.
It says.. primer not normally required but if it is then use Simoniz Acrylic Grey Primer... spray thin even coats at 20 - 30 minute intervals... will be cured after 72 hours... DO NOT OVERCOAT WITH OTHER PAINTS OR LACQUERS (their caps).
Hope that helps - I'm certainly going to try it when I next fettle those bits.