We have an older wooden 'feature window' and a friend made us a stained-glass insert to fit inside (there's a rebate there so the edges of the window press up against it, and it's currently held in place with screws) - so the existing double glass is there, then a 3" gap or so, then the stained glass.

There has been quite a lot of condensation between the original window (double glazed, about 20 years old but in good condition) and the stained glass insert. Insert doesn't fit very tightly, I am wondering if I should try and make it LESS tight fitting, so there's possibly more airflow, or should I try to seal it with weather stripping so it's totally airtight?

I could put silica gel sachets in the bottom, wouldn't look great but would be somewhat disguised by the border, or I could turn off the humidifier for a couple of days before I seal it up - we are in a very dry climate and without the humidifier the % RH often drops below 35%.

What is best, does anyone have any ideas?