70 Challenger
I have the First Place Auto repo T/A rear spoiler.
It has the floating mounting plates, and they don't seat and just want to twist and pull out before I can get the mounting nut tight.

Is there a trick to this I'm missing?

Thx

When you install the brackets inside the spoiler, you lock them in place with the push retainers right? Those usually hold the brackets steady while you tighten.

Yeah, I have the screw on retainers snug. The problem seems to be the bracket and underside of the spoiler are so smooth, they easily spin with the slightest torque.
To compound the problem, the molded indents are so small, they do nothing to hold the bracket straight.

With that bracket spinning as you say I can see your pain. Can’t do anything about the indents but if the bracket is bent similar to a “V” then the ends wouldn’t grab like they need too. If they are ok I’d try screwing on two 1/4 inch nuts behind the spoiler nut used to retain spoiler. Leave them close to the end and tighten them so they’re tight against one another and use these as a way to hold bracket in place as you tighten the spoiler nut.

Hopefully there’s enough room to tighten with a wrench.