I just had Dave Root work on my RV this week - if one is mechanically competent it is not a difficult task; just time-consuming. We had 5 windows done; Dave and his business partner arrived at my storage yard at 8:00 am sharp and were on their way home by 2:30 pm. It took the two of them about 15 minutes to remove the 5 windows from the RV, and about 15 minutes to re-install them. The rest of the time was disassembling the glass, cleaning all the panes, resealing and reassembling them, and waiting for the sealer to set up.
Could I do it myself? Probably. Would I want to do it myself? No - there are some things I prefer to leave to the professionals, and Dave provides a 3 year warranty on his work, which I could not provide if I did it myself. He makes several trips from his Bend, Or home base each year so you don't even need to move your RV to get the work done. For me, I don't mind paying him; others of course have different opinions...