I have a two piece rear section which is normally joined with nut & bolts but due to a (ahem) design change I need to permanently bond these panels together to maximise strength.
I will probably have to blend the panels after bonding to hide the adhesive line ...... but what adhesive do I use?

PU would seem to be a good choice but can I still blend the panels after bonding or will it just crack at the bond line?

PU would work, as would epoxy which is a better secondary bond than the PU but generally slightly more expensive depends how strong u want it suppose
Shug.

Fibreglass is the cheapest to use but perhaps more messy to actually do , depends how easy it is to get into where you need to join the panels.....if awkward use sikaflex as not so messy.

Epoxy doesn't bond too well to polyester. You could use a polyester ashesive though.

Ive seen the joins filled and blended using gel coat. With care it is possible to make it look one piece.

Thanks for the input guys - the panels are joined with a 30mm flange (and usually nuts & bolts). Two pack epoxy (Araldite or similar) should be ok then. I would use fibreglass resin but I think it will 'go off' a bit too quick for me and it's messy as hell - epoxy will give me 30 minutes or so which should be plenty of time.

If I get the positioning dead right I might make a feature of the join line but if it doesn't work out I can always blend it in with filler later. I am going to paint it anyway so I can wait and see what develops.