I'm getting close to the stage where I'll need to paint my GFRP bodywork (I'm leaving the ali un-painted). What are my options for a DIY job?

I have some experience painting GFRP with rattle cans, specifically a human powered submarine of which I was project manager during my final year at university. I'm wondering if there is a slightly more pro way of doing it however?

Just etch prime and spray with your paint of choice.
Plenty of advice on the mig-welding forum.

You do need a decent sized compressor, but the cheapish sprayguns do give good results. Do your research on what paint, I think you can get a plasticiser additive that may be handy (though that may only be for 2K stuff)

Getting a good pre any thing surface on GRP to work with in the first place would be where I spend most of my time, I use a DA sander with scotch bright type pad but a few hours spent using a lot of elbow grease may keep you fitter! Self etching primer for steel seems to work well as a base if allowed a day to dry then high build primer, cut it back and smooth with 1000 grit wet dry panel wipe clean. Don't forget that fine coats laid over a few sessions is easier to correct if it goes wrong than correcting the one big heavy coating that leads to runs. One day I will write that on the wall to remind myself!

Unfortunately not much help to you given your location, but these guys have a professional paint booth for hire and give lessons: http://ramp-it-up.co.uk/

Scuff with 600 paper, then a coat of Awlgrip epoxy primer.

Good enough for most commercial aircraft, and certainly most serious yachts.

Don't let the Awlgrip harden more than 4 days, or you'll be sanding forever to get a final paintable surface. Hard as glass. From too many years experience of the stuff, but I still keep using it, and it can't be bettered for most uses.

Cheers
Nev.

^^^what he said^^^ personally find epoxy primer gives a much better sealer coat and therefore better base for your top coat or base/ clear whatever you're going to finish with