My Tundra came with nice fiberglass tonneau courtesy of the original owner. It helped my high score of 22 highway despite the EPA sticker. Being a 4.7L 4WD model I suspect further improvement is high fruit. Still, it's fun to think and rethink possibilities. I sold that cover because it's not 5th wheel friendly. Removal, storage and reinstallation were solved problems but a lot of hassle. I have a
short cap that I may yet annex for off-towing season. Given other priorities and current situation right now, however, to just get through this Winter I'll probably just put my toolbox back on the front of the bed and close off the rest of the box to keep snow out. The short cap does create a blind spot that bothers my wife when she needs to drive it so in the grand scheme I'll probably have something to share about that mod before long.
Cheers
KB