I do drone and wildlife photography and totally get what you're looking for. I’ve been using the G2 by BakFlip for over a year and it's been awesome for transporting gear. It’s got a clean, low-profile design so it doesn’t draw attention, but locks tight when the tailgate’s shut. Keeps out rain, snow, and dust, which is huge when you’ve got cameras and lenses in the back. It folds up easily when I need to slide in tripods or larger cases, and doesn’t rattle or make noise. I found it through
https://bak-flip.com/ and it had all the fitment details I needed. Bonus—it’s light enough that I didn’t need help installing it. Really great for peace of mind on the road.