I have seen some pretty cool hydrolic in bed lowing "shocks" like what is used to raise and lower rear hatches on SUV's, with pin latches that secure the gate when closed. Here is something similar with tailgate supports that are hinged steet that fold close with the gate, vs. the shock/struts with a great install photo sequence!
How To Install Hidden Tailgate Latches - Classic Chevy Truck - Brothers Classic Truck Parts