1/2" angle aluminum from Lowes cut into 4 pieces.
Cut holes in the hood for the vents to drop into and use the existing
screw holes in the vents to screw into the angle aluminum. When you tighten the screws down, it tightens the aluminum bracket up against the sheet metal of the hood, holding the vent in tight.
A word of warning though, when I did this, the rain took out my TPS sensor. I think some sort of drain will be necessary. I can take pics if you need.