I'm about to repair a sash window with some rot along the bottom of
the top sash. This will entail removing the staff and parting
beadings, and whilst out I'd like to apply draughtproofing. I see
various companies supply kits which consist of new beading with built
in brushes to stop the draught.

There are various methods of advancing complexity and cost. The most
economical would I think be to rout a groove myself into the beading
and apply the carrier and brush. If my beading is OK I could do the
whole house this way for about £75 whereas buying kits would be £900.

Has anybody tried this?

If so which of the beading is the brush applied to, and what's the
best way to seal the bottom edge of the lower sash?