I am in the process of installing a square door 520, and have a question. What would be your opinions on cutting a new hole in the rear side for my furnace flue pipe? It would simplify my install if instead of having a couple 90's in my pipe run I could just weld up a plate with a thimble, and attach it to one of the rear sides. I would then just cap off the original flue exhaust and I could access the back chamber by removing the cap and vacuum it out periodically that way. I can't see any particular reason to not do it, although it might not scavenge the flue gases quite as well , but I have a ton of draft. Thoughts?