Has anyone tried construction adhesive instead of thickened epoxy for installing things like bulkheads and hatch lips.
Less expensive than epoxy and I find it easier to work with.

I wouldn't. Based on the mechanical properties, I definitely would not use it for high strength bonding purposes (padeyes, footbraces, bulkheads you push against or the like). According to it's white paper, it's properties are about 1/10 that of a thickened epoxy (like West Six10). For bulkheads with no stress on them? Maybe... It's not recommended for constant water submersion. You'd have to make sure everything was bone dry when you stored the kayak. With those thoughts in mind, I'd stick with thickened epoxy. In the grand scheme it's not much of a cost saver.