I've never seen a double pane window that didn't eventually fail....residential or otherwise. I guess it's just an inherent flaw int he manufacturing process. I just replaced the lower fixed pane on my driver's side window and low and behold, as I was driving the coach yesterday, I noticed that the passenger side is now starting to fog up.
I did find, however, that replacing the pane with a new one was more cost effective for me than having it repaired. My windows are Atwood and the replacement pane was $150. All the repair options were at least $250 or better, including the DIY kits that you can buy. It DID take me about 3 hours to do the job, but that's because I've never done it before and had to feel my way around while doing the job.....on the job training I guess.
I would suggest that you add to your list of options a phone call to the manufacturer of your glass panes and see if there's a replacement option for you. If you're handy and can do the work yourself, you might just find it more economical to replace rather than repair.