$3.00 got me a new looking (and smelling) pair of HellyHansen polyurethane coated rain pants big enough to get on over work clothes at my favorite second-hand shop. These will be for biking to work as well as hiking, so I must add ventilation somehow. The pants are simple: elastic through fabric casing at the waist, no pockets or zippers, snaps to snug up the leg at the hem, taped seams.

Would it work to cut the inner leg seam and insert some kind of mesh from knee to knee? What mesh would work best, and where might I get it?

Could I remove an inverted triangle of material front and back just below the elastic casing to make 'chaps'?

What else might work?