Alot of people use aluminum angle as marquee retainer which is alot thinner than the HAPP stuff.. I have the hap stuff for mine.. but its WIP so hasnt gotten there quite yet..
This is what I used. It's actually aluminum bracket designed for suspended ceilings. The store I bought it from called it a "Suspended Ceiling J-Bracket"... I used a good pair of tin snips to cut a clean edge, and used a corner to fold it into a 90-degree. It looks good once painted, and it's terribly cheap...
It came in an 8-foot length, which was enough to do a test/rough mock up, and a final, clean one for my cabinet.