my home was built in 96 and is all HURD Al clad wood casement. The 2nd floor of my house which is typically cooler because our MBR is on the 1st floor and we don't go up there all that much, last winter in one of the bedrooms I pryed off a window casing to find minimal batt insulation stuffed between the window and stud frame. There was actually a frost layer on the window frame exterior in the gap, so I melted it, dried it out and put expanding foam in. This helped the frost on the bottom inner portion of the pane but did not eliminate it. The moving portion of he casement has a crappy weather seal on the perimeter, I want to try something like thishttp://www.amazon.com/Frost-V23WA-Extre ... B000OZT84K
only I need it to be roughly 5/8" thick overall, and haven't found it yet.
Another Idea I had was to build an interior storm window that goes in the screen track out of thishttp://www.amazon.com/gp/product/B000L0 ... 00_details
and some lexan, but I haven't had a chance to try it yet. My wife got sick of waiting and just shrink wrapped the windows in our MBR and bath which are mostly exterior walls. Since shrink wrap makes such a huge difference I know the windows are wicking heat away like crazy.