The easiest and cheapest way to make one, is go buy a Rubbermaid tub, preferably black and cut out a rectangular piece that is long and wide enough for your application and use 3m double side tape, to tape it onto the light.
I hope you are able to make a good sheild. I have seen some installers make sheilds, there is still some flashback. So far the light I have seen with no flashback is the tomar 200s. I have a duel avenger R/B and I still have flashback. Mabey you can put the slimlighter in the rear and get another light for the front.
when i made mine, i positioned the light exactly how i wanted it and then made the shield to fit perfectly almost against the windshield. I gave a slight bit of room for a rubber piece to press up against the glass so i wouldnt get the tapping. That is why i never stepped up and said i would make a flashback shield for them because each car has a different pitch with the windows and depends on how you mount the light etc. Just to give you an idea, this is how mine looked almost done. I was tesing it out and all. I also had to customize it for the rvm being it has a power cord that goes to it..
that was my amateur days of things lol the little lin 3 was ok.... you could see it lol. Im thinking of putting it back up with my intersection light i made in the middle where the lin 3 is and then a dual talon on either side and have a true custom interior bar lol
Holy $H!T lol so i wasnt the only one with the idea. The only thing is mine was mounted to the shield because i was not opening the slimlighter to perm mount the ighthead to the slimlighter. Still the idea... hey whenen.... new version of the 3 head inner edge.... lol