There is another thread about a year old that discusses the Hehr windows and associated problems--with helpful advice from Wingnut on how to replace. I have 16 windows; 4 were badly fogged and replaced by DRV under Hehrs first warranty deal. I am waiting for 6 more which will arrive shortly, costing me labor and freight. Thats 10 windows bad out of 16 or 62% in less than three years. I fulltimed in two other fifth wheels for 12 years before my MS with double panes that never fogged.
While its tempting to blame the problem on the switch to frameless, both of my framed windows on the end of my LR slide are fogged.
MS 2010 36tk3
2006 3500 Duramax