Using a tonneau cover

I have had 2 trucks with 2 different covers, both of them roll up styles. They never leaked or pooled water because they have bars in them. The first was an access brand the other a mopar. The access brand gave me clearance issues between pin box and box sides because the rails for the cover are clamped on to the insides of the box, so it reduces your bed with about 5-6". The mopar rails clamp on top of the box sides so pin box to box clearance is not an issue. If you buy a cover no matter what brand just make sure the rails that they use are clamped on top of the box sides.