80's M? 320 rear spoiler, how to make it stiffer?

[NOMAD]

Anyone have a spoiler that is the rubber material and raised up off the deck?
There is one I thought of picking up that is raised but it is a bit loose feeling and seems like it would bend or vibrate at speed. It has three legs total.

Any way to make it stiffer? Insert something in the bottom of it?

[E30_fiend]

I dont have one but I would think that you could stiffen it from the sides. Insert rods from the ends and push them in.