http://www.newgel.com.au/datsun.htm

I have the rear spoiler shown in the above link's pictures,

It does not have any designated bolt holes,

What i was thinking of doing was attaching it with 2 bolts at either end and using some water based polyurethane all around it,

That should hold it right?

The old Ferraris used pop-rivets on the early ducktails.

Some of the spoilers have bonded in risers or areas for screws to bite into through the sheet metal, some have holes for access that are filled after installation, and some are just bonded on using epoxy resin

Unfortunately my car had one of those spoilers on when i bought it. It has self tapping screws up through the hatch. 3 at eiter end and 4 across the centre and was also sealed with some sort of butyl putty.

It was very difficult to remove so I doubt it would have come loose in normal driving.

See the pics for the before and after. You can see where the screws went and the damage to my paint job. Welding holes in the hatch is not easy either.

Warren

I used that black silicone. I think it's called SICAFLEX from memory. Man that stuff is strong. It's never shown any sign of budging! No holes in the hatch.