I have a 2003 Winnebago Adventurer and as you can see by the attached photos, the slant window on the driver door fogged up. Atwood mobile products in Indiana was contacted (address and phone number in my last photo). I already had the part number for the window which was found on the Winnebago online site. The Winnebago parts catalog lists every part on the RV even down to the screws, nuts and bolts. I gave Atwood the part number for the window and they forwarded an email with the window measurements. I verified that it would fit and ordered the window. $150 plus about $40 for shipping. A local RV repair shop had the butyl tape I needed to hold the window in place.
Again, as you can see by the photos I began by removing the rubber seals along the outside edge of the window. They basically just snap in place and a small screwdriver is all you need to pry them out. Using a screwdriver and a straight edge razor I pried the window out. There were two small rectangular plastic spacers on the bottom edge of the frame. I removed those and cleaned them off. Using mineral spirits and the straight edge razor I cleaned the old tape off the metal frame. I got probably 95% of the old tape off. I didn't bother with what was left in some of the nook and crannies.
I placed the new tape in the metal frame and replaced the two spacers on the bottom edge of the frame. I just pushed the spacers into the tape.
I replaced the window by resting the bottom edge of the glass on the two spacers and then pushed the window into the frame. I pushed the glass along the edge where it made contact with the tape to make sure the glass made a good seal with the tape. I made sure the glass was seated with enough space so I could replace the rubber seals and pressed the seals back in place. The rubber seals stretch a little and you have to make sure you don't pull on them otherwise they won't sit properly against the window.
All this was done at a fraction of the cost of paying someone to do it and I think I had it all done within a couple of hours.