Rooftop cargo box or bag

Any suggestions for a NARROW box or bag that can fit next to a kayak on a small car? Will carry camping gear. Width 24" or less, length four to five feet? Safety important, of course. Aerodynamic is good too. Kayak is carried on saddles so there’s not much space left.

Not a specific model, but Thule and Yakima both have some relatively narrow boxes, often geared toward skiing.