We have a Silverado 1500 Crew-cab with a short bed and we are able to carry 4 Kayaks, which are 10' each. We strap the front of kayaks down on bottom of truck bed and the back end of them on top of the closed tailgate, which allows just enough clearance for tight turns. We use 3 x 12' tie-downs.
We have been able to get 4 bikes on as well, 1 on each side standing up. One small bike along tailgate under kayaks, and one on top of kayaks with a blanket between. Also firewood tucked underneath.
Amazing what one can carry if you try.
Dean