Hard tonneau or soft? Does your tonneau completely cover the bed rails? I had a soft cover that did not fully cover the rails, so I was able to mount Yakima tracks on the bed rails using blind bolts, then mount crossbars. Once you have that set it becomes just like any other roof rack. If possible, I would go with a wheel-on mount system rather than a fork mount. Dealing with loose front wheels is a pain. I have modular trays from 1UpUSA and love the sturdy build. American made and no plastic.
If you have a hard cover I would make sure it is strong enough to take the side to side wobbling that all bike racks do. Maybe mount a piece of flat aluminum or hardwood on the underside of the cover and bolt your rack through that.
I toyed with making some DIY crossbars out of unistrut, but for only $150 the above bars seemed like a great deal assuming they are decent quality. I will update once I get them and see what the quality is like!