Did you detect any reduction of Rx or Tx signal because of the PP box. This is a very good idea: there are many different sizes of box available.
73 Mike G4CDF
The upside-down cheap food-box is made of Polypropylene PP5 and after being microwaved with >500W RF it stayed cool! (however, it has no microwave safe mark. This plastic is very sturdy, so sawing-drilling is easy. Only made RL-measurements with the "boxed" Helical feed in the feedpoint of a dish, measured abt 25dB at 2400MHz.
Performance with my current 1.1m offset dish and abt. 3W at the Helix is very good, but could still be interesting to measure for any reduction on 2.4GHz and also for 10.5GHz using this type of weather-protection. I will come back on this.
73 Ed PA1EW
Update: I did test today using the PP5 plastic lid from the box. Placed in front of my LNB and checking the lower beacon I could not detect any signal reduction!. So 10.5GHz seems not bothered by polypropylene 5 plastic sheet, at least very little.
An advantage of the upside-down box is that there is no condensation problem with the open underside.