I've got a storm window which has pretty severe rot on the lower rail. I've never tried to repair a window before, so I'm not entirely sure how to proceed.

I've not yet tried to remove all the rotted wood, but it looks to me like about 1/4" of the bottom is completely bad, the tenons have completely rotted, and either side (where the tenons attached) is rotted between 1/4" and 2". The side rails with the mortise are in better shape, but would need a little restoration as well around the mortises.

My initial thought was to remove the paint, remove all the rotted wood, seal with one of those penetrating wood hardener products, and then rebuild the rotted edges with epoxy. I could then fill in the mortises with tenon blanks (or maybe just epoxy?) to make the side rails solid, and then rejoin the lower rail with dowel joints. The only thing I'm unsure of is if that is going to be using too much epoxy?

Option B is to completely replace the lower rail, but these are old if not close to original storms (the house was built in 1925) so I'd rather preserve the old wood than replace it if possible.

Has anybody else dealt with this that can give me some tips?