If a bed liner gets in the way during installation, just cut a notch where you need to fit a clamp or other cover part. If the bed liner wraps over the rails and your tonneau cover lies between rails (instead of above them), the two parts might not both fit on your truck. Most bed rail caps won’t affect installation, but diamond plate bed rail caps will prevent some covers from fitting, or from forming a weather-tight seal.
If your cover does not come with rails, the cover itself should have clamps that swing down from the underside once the cover is in place. [1] X Research source These covers are less stable and not weatherproof, but easy to remove and reinstall. If you have a retractable tonneau cover, which comes in a canister, you may need to position this before you place the rails. Put the canister on the edge of the bed rails, next to the cab. Center this perfectly before you attach the rails to the canister. [2] X Research source
If there’s a large gap (more than about ⅜ inches / 10mm), you might need shim brackets instead. Unclamp the rail, slide the shim brackets onto the end, space them out evenly, and reclamp the rail. [4] X Research source Your kit may not come with shim brackets, or may have shim brackets that attach with a slightly different design.
Some soft tonneau cover instructions recommend skipping this step until the end, so you can make final adjustments more easily. Don’t try this for a hard cover, which needs a firm
If there is a gap between your bed rails and the cab, the side rails should not extend into this gap. The rails will not necessarily be level with the closed tailgate.
Some tonneaus come with additional seals for the sides or tailgate, and/or larger corner plugs to weatherproof the rear corners.
Storage straps, fed through holes in the cover. Tension adjuster screws, for hand tightening of the cover. These usually attach to the side rails, and may come pre-installed. Hinged covers and some hard folded covers include a rod to prop the cover open. This should snap or screw into place somewhere on one of the side rails, with the other end resting on a small cradle.
If you cannot center the cover, place it back on the ground and readjust the rails. Hinged hard covers (one solid piece without folds) are extremely heavy. They cannot be installed safely by a single person. Use a forklift or several helpers. [7] X Research source
Look for a small hand-tightened screw on the rail to adjust cover tension. It should lie taut across your bed, completely covering it.
Some covers have clamps or levers on the underside, which lower to brace the cover against the bed side.
