I widen the beam holes on the outer foam box.  Now all the holes are ~ 0.75" in diameter.

We are concerned about the scattering on the insulation, so we decided to increase the holes' size.

I used a heat gun to heat up a steel rod to melt the foam panel. 

As the insulation box was opened, I checked for scattering light inside the box. I did not see any scattering ligth except

on the ACAV inner insulation opening.

Also, there is a little scattering light at RCAV's insulation cap, so I measured the beat noise when I opened RCAV's inner cap.

There is no significant change, see fig 1. The trace with higher noise was taken when I opened the cap, probably because of too few average.

The scattering on RCAV cap might be negligible for now.