Although the HEPA + Carbon filter seems to be working just fine, I decided to add an exhaust fan to the printer enclosure. It uses the same fan as the filter but discharges the air into a 2 1/2" hose which is then sent though an unused doggie door. I made a panel to go in the doggie door which the hose can attach to with a quick change coupler, and a cap to close it off when it's not being used. Seems to work, and the volume of air at the end of the hose is reasonable for what I want it to do. I did find several design problems which I went back and corrected as best I can, but I feel that if I had started over from scratch I would have done things a bit different with the exhaust fan. It is not enough of an issue for me to spend that time though, and since it works I probably will just leave it be. I've not posted this, or the doors or most of the rest of the enclosure on Thingiverse yet, and hesitate to do so since although I like it, and it works, it is not perfect - and is also not complete yet. It has also been an expensive project.
My mission is to lower the collective IQ of teh Internets one post at a time.