Another adhesive to consider is the relatively new 2-part, 5-minute epoxy for use on PVC material.
Usually, little or nothing will stick to PVC. That's why it's an excellent material to use for plumbing drain lines. Slicker'n scum off a Louisiana swamp, it is.
Consider a slight rough up of the cowl components prior to the bonding experiment. I've used it. It will work. There just seems to be lots of built-in stress within that instrument cowl 'cow's tongue'.