I have a GW 100. Just installed it last year. I now have the side panel off of it to clean and inspect the unit.Very dirty,i was shocked. Dont know if it was ever cleaned before I got it. I have boiler brushes and can clean the tubes well,and suck out the left over dust. The questions i am posing to other GW owners is what do you use for the insulation on the sides? Reuse what was there? Or install new? If so what can be used safely? Now I have heard some people have cut axcess doors or panels in the side cover to have quick axcess to clean the tubes w/o taking the sides off. If you have done this can you post pics please. Thanks