I would use 11FC for that.
Note that the aluminium sail track will expand and contract with changes in temperature (could be easily 50C from coldest to hottest) quite a lot more than the fibreglass, so the Sikaflex needs to be quite thick, maybe 2mm at least, between the track and the fibreglass otherwise it will tear.
You can do that by using small patches of double sided adhesive foam tape folded to get the thickness. It will also hold the track in the right spot while the Sikaflex goes off.
Surface preparation needs to be really good.
Cheers,
Peter