If anyone is thinking about lader racks, I took advantage of the July 4th sale coupon at Harbor Freight to buy an aluminum ladder rack. Original price of $299 was lowered to $239.
Installed on a 2018 Colorado, distance front/back (center to center) between the crossrails is 5’ 9"; crossrail width is 66", with 6" overhang past upright support; roof clearance below top of rail is 8", with 1 1/2" clearance for antenna. The top of rear crossrail to ground is 81" and top of front crossrail to ground is 79"; top of crossrail to truck toprail is 28".
This rack appears identical to a brand sold elsewhere for $379. More expensive brands appear to have streamlined fairings around the brackets. The cosmetic upgrade on the other brands, which also includes adjustable aluminum tie down brackets vs. the realively sturdy composite with this rack, are probablly worth the additional cost. However, reviews indicate the Harbor Freight model is strong and quiet, without whistling at highway speeds. Additionally, the Harbor Freight model can be cut down (4" to 6") to reduce loading height. (I plan to try it out a few times before attempting modification: make a clean, square cut on upright supports; drill a new hole through the supports for the 10mm cross bolt that secure the brackets; use a 10mm tap to recut 40mm deep into the two round channels extruded the length of the support, that go through the top of the bracket into the support).
There is one issue in common with any clamp on rack. The Colorado truck bed has 9" box section in each corner. Since the L-shaped rack mounts are 13" long, the two C-clamps that attach the assembly to the truck bed lip only have room to if placed next to each other. While that is probably acceptable, I plan to drill a hole closer to the upright support for a bolt through the bracket into the truck rail. An M10 rivet bolt or jack bolt (Grangers or on-line), is a sleeve bolt that inserts into a tight hole in the sheet metal. The sleeve is crushed using a rivet tool or a bolt with an oversized nut with washers between the bolt head and the sheet metal. If properly set, it provides a fixed nut that wont spin.
Note: I’m reluctant to do any modifications for three reasons. 1) It would void the warranty. 2) Lowering the rack and changing the airflow could rest in whistling at highway speeds. 3) Lowering the height would expose several inches of the antenna to potential damage.
This rack can easy hold two 145 Tsunamis (my model is 24.5"). Carried deck down, the cross rails hit on the hatch covers where the lips provide a somewhat reinforced, flat area of the rubber hatch which helps prevent sliding. I put the tall adjustable tie downs in the center of the crossrail, lift one end of the boat and let it stop against the tall stop, then lift the other end. I attach the tie down directly to the crossrail, pass the rope through the tie down, over the boat, and under thr crossrails.
When tied down, even without crushing the deck, the boat doesn’t shift. Gripping the hull and shaking the kayak moves the entire truck. Extremely satisfied and consider it the best value available. It comes with four string composite tie downs. A set of four aluminum tie downs from another manufacturer can be ordered on line for $34.