GMC Sierra Truck Caps | Premium Fiberglass & Aluminum Toppers
Our CX-Series truck cap is engineered specifically for GMC Sierra 1500, 2500HD, and 3500HD short and standard bed configurations. Built from vacuum-bonded RTM fiberglass, the CX matches your Sierra's contour lines and paint code for a factory-appearance finish. We mold each cap with reinforced mounting rails that distribute weight evenly across the bed, preventing stress cracks and ensuring decades of reliable service.
The frameless rear door opens wide for full-bed access, and the side sliding windows feature our dual-pane tempered glass with integrated screens. Every CX-Series cap ships with our OE-style central locking system that keys to your truck, three-point weatherstripping, and carpeted interior headliner.
What makes our Sierra caps stand out
Materials & Construction for Sierra Applications
We manufacture truck caps for GMC Sierra in two primary materials: vacuum-bonded RTM fiberglass and welded 6061-T6 aluminum. Our fiberglass CX and MX-Series caps use resin transfer molding that embeds fiberglass mat into a two-part epoxy resin under vacuum pressure, eliminating voids and ensuring uniform thickness across the entire shell. This process creates a one-piece monocoque structure stronger than hand-laid fiberglass and lighter than equivalent steel.
The Z-Series aluminum cap frame consists of extruded 6061-T6 alloy corner posts and roof rails riveted to .090-inch marine-grade aluminum skin panels. Aluminum resists rust in road-salt environments and won’t crack under flex like brittle fiberglass can in sub-zero temperatures. We powder-coat all aluminum hardware and apply a durable two-stage finish to fiberglass caps using automotive-grade basecoat and clearcoat matched to GMC’s factory paint codes.
Mounting & Fit for Sierra Bed Configurations
Every ARE truck cap ships with application-specific mounting rails machined to fit Sierra’s bed channel geometry. The 2019-newer Sierra 1500 uses GM’s CarbonPro carbon-fiber composite bed on higher trims, which requires our updated nylon-insert clamp system that distributes clamping force without crushing the composite bed rails. Sierra HD models retain steel beds and accept our traditional C-channel clamps.
Bed Length Options
We build caps for all three Sierra bed lengths: short bed (5 ft 8 in, crew cab only), standard bed (6 ft 6 in, available on double and crew cab), and long bed (8 ft, regular and crew cab). Measure your Sierra’s bed from the inside of the bulkhead to the inside of the tailgate to confirm length before ordering. The cap’s front bulkhead must align within 1/8 inch of the truck cab for proper weathersealing and load distribution. Bed-length mismatches void our fit warranty and create dangerous overhang.
Locking, Security & Weather Sealing
Our central locking system on CX and MX-Series caps uses a five-pin tumbler cylinder keyed to match your Sierra’s ignition key at time of manufacture. When you provide your GMC key code during order, we cut the cap lock to your existing key so you carry one key for truck and cap. The cylinder drives stainless steel rods that actuate rotary latches at three points on the rear door, providing 1,200 pounds of pull resistance against pry attempts.
Weathersealing relies on three-component bulb seal extrusions that compress when the door closes, forming a continuous barrier against rain, snow, and dust intrusion. We mold seals from EPDM rubber compounds rated to remain flexible from -40°F to 160°F. In freeze-thaw testing, our seals maintain compression set below 15 percent after 10,000 cycles, ensuring long-term weatherproofing even in harsh climates. The same EPDM bulb seal runs along the bed rail contact surface where the cap mounts to the truck.
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Common Questions About GMC Sierra Truck Caps
No drilling is required. Our Sierra caps use clamp-style mounting hardware that secures to your truck's existing bed rails. The C-channel clamps slide onto the bed rail and tighten with stainless steel bolts, distributing clamping force evenly without penetrating the bed floor or sidewalls. You can remove the cap and restore your truck to stock configuration at any time without visible holes or permanent modifications.
Yes. We updated our mounting hardware in 2019 specifically for Sierra 1500 models equipped with GM's CarbonPro carbon-fiber composite bed. Our nylon-insert clamps prevent crushing the composite bed rails while maintaining secure attachment. Specify CarbonPro bed when ordering so we ship the correct clamp style. Sierra HD models retain steel beds and use our traditional clamps.
We offer paint matching for 40+ GMC factory colors across all Sierra model years. Provide your truck's paint code during order (found on the driver door jamb sticker) and we'll mix basecoat and clearcoat to match your specific color. Tri-coat and pearl colors require a slight upcharge due to additional paint layers, but we can match any OE Sierra finish including limited-production colors like Glacier Blue Metallic and Cayenne Red.
Static roof load capacity is 300 pounds for fiberglass CX and MX-Series caps when using our optional crossbar kit. The Z-Series aluminum cap supports 500 pounds dynamic load with the HD crossbar system installed. These ratings apply when the truck is parked and the load is evenly distributed. Reduce maximum load by 40 percent during highway driving to account for acceleration forces. Never exceed your Sierra's gross vehicle weight rating when combining roof cargo with bed cargo and passenger weight.
Our fiberglass caps carry a limited lifetime warranty on the shell against delamination, cracking, and structural failure. Hardware components including latches, hinges, struts, and weatherstripping are covered for five years from purchase date. Aluminum Z-Series caps have a 10-year frame warranty and five-year finish warranty. Paint and gelcoat are warranted against fading for three years. Warranty coverage requires professional installation or adherence to our installation manual if you self-install.
Yes, but order our reinforced floor option when you purchase the cap. Standard caps are not engineered to support the concentrated loads generated by fifth-wheel towing. The reinforced floor adds two additional crossmembers beneath the cap that spread hitch forces across a larger area of the bed. This option is available on CX-Series and Z-Series models for Sierra 2500HD and 3500HD applications only. We do not recommend fifth-wheel towing on light-duty Sierra 1500 with any truck cap installed.
Yes, if you provide your Sierra's key code when ordering. We key the cap's central locking cylinder to match your truck's ignition key at the factory, so you'll carry one key for both. If you don't have your key code, we can ship the cap with a standard lock and provide instructions for a locksmith to rekey it locally. The MX-Series electric liftgate model also offers a remote fob module that pairs with your GMC key fob for hands-free entry.