Hi Diana,
I don't know what causes dual pane windows to fog nor if they can be repaired. I can tell you that you likely could have them all replaced wth the frameless-style windows but it would be quite costly. Probably $3k-$4k shipped to CA and installed (all just a guess).
Is your glass Kinro or Hehr? If it's Kinro, please give Lippert a call (574.537.8900). They will likely want your VIN, so have that ready.
On edit: Lippert purchased Duncan Systems and I see they do fogged window repairs. Though they are in Elkhart, IN and you're out west, it may be worth calling them to gather information.
On further edit: Found something online that talks about how/why dual pane windows get fogged.
I'm not saying this info is accurate, but here's what "they" say:
As the inner space heats up, the inner air expands and is forced out of the compromised seal system. When the inner space air cools and contracts, humidity-laden air is drawn in bringing baggage with it that is deposited on the interior glass surfaces (usually turning into a white cloud look). RV failures seem to be between four and seven years
It appears they sell information on a process they've worked out to defog windows.
Here's a link to their site.