I would try to get some gelcoat from Jeff as it is a slightly grey colour. If you use white you will notice it forever. However the stuff he has is a very runny consistency and is therefore not suitable for filling in dents or big chips. You will need a filler to do this instead, I think that I have used Plastic Padding gelcoat filler first and finished it just below the surface, followed up with a thin scraping of Jeff's stuff to finish it off.
The other option is to contact Kev Clark who is very good at repairs and you may get advice/help from him and possibly some of the stuff quicker than you will get it from Jeff.
Ian