I was thinking about adding an extra "pane" to some of our windows in winter. This would be similar to how those plastic shrink-wrap kits work, but I'd using something more permanent like a simple piece of plexiglass with a rubber strip on the end to hold it into the inset of the window. (Perhaps something like an interior storm window. Does this make sense to do? We've already got triple glazed windows everywhere (except on one door and WOW can you feel the difference) but thought one more layer might help. In our old house (very drafty, with single-paned windows) I used to put Roxul in garbage bags and fit the 'blocks' into the window sills of windows I might not miss so much through winter (basement, mostly). That helped enormously but in this case I don't want to black them out entirely but would like to reduce heat loss, too. Thoughts? Thanks!