Walmart offers Hyper Tough, Full Size Truck Tailgate, Bike Rack Carrier Protection Pad, fits 5 Bikes for $34.31 (orig. $89.98.  Free shipping with Walmart+ or on orders over $35.

Product Description:
Hyper Tough, Full-size and mid-size Truck Tailgate Pad, 56 inches wide, allows transport up to 5 bikes; quick and easy to install. Slots along with heavy-duty strap secure bikes for safe transportation. Truck Bike Pad Protector, the soft inner lining of the truck tailgate pad is made of soft and thick flannelette, which will not damage the paint of the truck, the outer layer is strong, durable, rainproof, UV resistant. Roll up flap cover allows use of the backup camera while in use. Additional uses, hauling wood, canoes, and other large objects. Convenient storage, with two tool pockets. Made for exterior of tailgate.
Hyper Tough, Full Size Truck Tailgate, Bike Rack Carrier Protection Pad, fits 5 Bikes:

• Tailgate Bike Pad with concave slots that can secure 5 bikes
• Carries up to five bikes including Mountain Bikes, in a pickup truck 
• Made of soft flannelette to protect the tailgate from scratches, which is thick and will not damage the paint of the truck
• A rugged nylon strap  will allow you to secure the pad and allow to the transport of bikes securely
• The outer layer is made of PVC laminated cloth, wear-resistant, rainproof, durable, and moisture-proof to protect the exterior of the truck tailgate
• Clips to allow you to roll up the flap and allows access to the tailgate  handle  while the pad is attached and access for backup camera
• Padded protection can haul a load of lumber, ladders, kayaks, canoes, and much more  with no damage to tailgate