Those are all good suggestions. Since I have an aftermarket box heater this is what I thought I would do. Go to the local hobby store and buy several packages of sculpty. It is a kind of synthic clay. Make a backing board, mash all of the sculpty together and then mash it into the louvers. Carefully pull the contraption out smooth the rough spots, then bake the sculpty. Now you have a mold of the louvers. I plan to push the sculpty in untill is just stands proud of the outside of the louvers. Once baked I will grind, file, sand the sculpty. Then coat the sculpty with vasilene. mix up some plaster of paris, and make a positive mold. Then coat the mold with grease or mold release, and fill with black silicon. You can put a backer of some sort on the silicon while wet to mount it in the proper place. That is my explanation, here is is my logic. once done and in place the silicon will act as a plug in the louvers, being slightly oversize it will fit very tight, and using black will make it appear to be un filled original. I know it is complicated, but if you or I find a great deal on a fresh air heater then it isn't a chore to pull the plug and install the heater. Any comments or suggestions are welcome.
