I've had both, my current ranger has a spray in liner. The 96' ranger I had before had a drop in. Rust is not a particularily huge issue. Biggest difference is with a spray on you still get to use your bed rails for tonneau mounting or eyelets. The plastic drop ins use the bed rails to secure themselves snugly... It was a major PITA when I would need to use the cap, as the liner had to come out and the cap fitted. With the spray in its just plug and play...