my buddy has the same problem. We were in my truck, and he threw his beer cap into the bed, and it slid across my toolbox and tinked onto the pavement as we were driving away from my religious sister and her friends after we changed a battery in her car. she was impressed, needless to say!
But to stay on topic, I voted slider, considering the cost wouldnt be much higher. the ventilation and ease of access to the bed is worth it. Crooks will get in if they want to, and would prolly break a window on an unlocked door. nothing stops those guys...except rusty trucks with nothing in the cab!
Used silicone to convert a slider to a non slider... to stop the annoying buzz-rattle from the slider due to uncorrectable drive shaft vibration. It is another place for leaks, noise, and repairs. Not my first or second choice to get one if I ever have to.