I need to make a flat fibreglass panel approx 110cm x 80cm for my baja style roof rack which I had made and never did anything with.
What would be best to use to layer it up on to get a good shiney finish. I don't want to use the glass dining table in case in doesn't release properly. I would of tried that when single but wouldn't chance it now

see if you can get a commrcial body builder near you(makes waggon bodys)they will have sheets of glassenite.as well as sheets of grp.

MDF is pretty flat, well coated should release well and dirt cheap

Can you not buy a cheap picture/poster frame (many about that size) and then just trash the glass if it doesn`t release?

think my brother wanted a flat panel, believe he used  conti board from b and q, you know, the plasticy covered wood stuff for shelves and wotnot,
dont even think he bothered with a release wax, just a pry bar/chisel, just slap on the gel coat, then several layers of matting, wait till its cured, pull it off,

I've used conti board before and it's not smooth so you get a mottled effect which is fine if it's not on show.
Looked on eBay for a second hand glass table and there are a few local for less the a fiver so may go down that route.
If I do will it release ok or stick?

You shouldent get a problem releasing from a glass sheet just watch you dont overlap on the edges and get the fiber wrapped around it. Get a good releasing wax, 3-4 coats of it, clean the glass/table throughly, smear first coat make sure it goes evenly all over, wait 20 min or so between each next coat or basically till each layer goes hazy like polish does, then a final light buff to smooth over the haze and i mean light you dont want to remove the wax, when i do any forming i use honney wax release agent on any material i'm laying up on and little plastic wedges like what you get in a wood flooring kit to pop the form and mould apppart.
Rich.