ADV Fiberglass 2019-2021 GMC Sierra Bedsides

Bed Length

2019-2021 GMC Sierra Bedsides

2019-2021 GMC Sierra bedsides, hand-laid in the USA. Price includes set of two bedsides (driver and passenger side). Fiberglass bedsides (5.5’ Bed Only) come standard in semi-gloss white. Fuel fill area built in. Bolt-on installation.

Our fiberglass bedsides for 2019-2021 GMC Sierras are handcrafted right here in America to ensure the kind of quality, durability, and craftsmanship you’ve come to expect from Advanced Fiberglass Concepts. Each Sierra fiberglass bedside is made specifically for your model and year and designed for a seamless transition between the factory panels and our aftermarket body panels. These GMC Sierra prerunner bedsides are a perfect match with our 2019-2021 GMC Sierra fiberglass fenders to create a build that is ready for any terrain.


  • Allows for larger tires without rubbing issues
  • Fiberglass bedside is hand-laid in America to ensure quality
  • Molded specifically to replace Sierra bedsides
  • Designed to be long-lasting even during the toughest rides and climates
  • Made in the USA
  • Comes standard in semi-gloss white
  • Part Number: AFC 173 (5.5' Bed - 4.5" Flare 2" Rise)

Installation Instructions:

All of our products are fairly easy to install. You will need a few hand tools and a few hours of time, depending on the products you have purchased. Also, you will reuse most of your stock hardware during this installation—it is typical to have a few screws and bolts left over, however. Advanced Fiberglass Concepts LLC does recommend that a professional install for a seamless fit install these products.

Tools required for most installs:

  • Socket set
  • Drill and drill bits
  • Screw drivers (Flat head and Phillips);
  • 120 grit sand paper (optional)
  • Metal Shears or Sawzall or Plasma Cutter

Although this is not necessary, we always recommend removing the bed to make the process easier

Step 1: Remove the taillights, as well as the bumper.

Step 2: Use a spot weld cutter to remove the factory bedside spot welds, which are located around the bedside.

Step 3: Once the stock bedsides have been removed, the inner bed structure will be showing and then it is time to mount our fiberglass bedsides. Best way to start, is by hanging the new fiberglass bedside over the bed rail.

Step 4: Align the fiberglass bedsides with all the bodylines on the cab and the taillights. You may have to sand or trim off the inner bed or fiberglass to get it into the correct position.

Step 5: Once you are happy with the alignment, it is time to bolt down the bedsides. We recommend our customers to use 4-6 evenly spaced bolts along the inner bed rail, one between the cab and the bed, and 1-2 bolts around the tail light area. Drill holes out with a 3/8 drill bit—the reason for this is so you can move the bedside back and forth to align the gap. Once you have the gaps spaced, tighten down the bolts. Do not over tighten! The fiberglass bedside will make sounds like it is cracking—this is common as it is fiberglass, so do not worry.

Step 6: Now as the last step, it is important to secure the front and rear portion of the wheel well. There are supports in all trucks, although you can modify your old mounts to work with the fiberglass bedsides or you can fabricate your own custom mounts.

You will need to be patient to get a good fit. You may need to sand some of the bedside down for desired fitment. This is because fiberglass bedsides are thicker than steel.

Please keep in mind—although all of our products are made from factory steel fenders, hoods, and bedsides, there is a difference in fit because of the thickness of the fiberglass compared to steel. Therefore, please be patient when you start this job.

If you need further assistance with this installation, feel free to call us—one of our techs will be more than happy to help you.

These instructions are useful for all bedsides sold by Advanced Fiberglass Concepts — therefore some of the steps may not be needed or should be slightly altered to suit your particular vehicle and product needs.