Fifth wheel trailer hurricane in truck bed
 

What to make of the fact that when towing a fifth wheel travel trailer, with the tailgate installed, anything in the truck bed that is light enough to be picked up by a person can be picked up by the air flow in the bed? Most fifth wheel owners find this out the hard way on their first trip. :)

This must be a bad thing aero-wise?

Some people pull fivers with no tailgate, and some with a vented tailgate. I haven't tried either. If I do, and the hurricane disappears, does this mean anything from an aero point of view?

What if the hitch could just emerge from a bed cover, would the bed cover reduce drag? For instance, imagine a modified gooseneck hitch arrangement, in place of a fifth wheel hitch, where the ball is at the top of a bed cover. If it could be mechanically sound, do you think it would reduce drag?

Something I like to believe, and your post makes a good opportunity to put it out there. I consider the amount of energy it would take to create the amount of turbulence you speak of, like a big fan, how much power would it take to run the fan? This applies to the vortex generation behind a car as well, the amount of power used to "spin" the air is just wasted. The energy required to move the air is an extra load placed on the engine of the vehicle and knocks the heck out of fuel efficiency.

I think a simple straight deflector from the cab roof back a couple of feet would kill it. I will have the opportunity to test that out this year.

The trailer is not a gooseneck? Either way, I'd make a bed cover out of some plywood or an aero topper with coroplast or fiberglass.

5th wheel = gooseneck

A 5th wheel and a goose-neck are technically very different. A 5th wheel has a much larger overhang that doesn't extend to the bed of the truck. A goose-neck has far less surface/frontal area, and the hitch extends all the way to the bed of the truck. If not properly accounted for, I have to imagine that the 5th wheel would have a far higher aero penalty than a goose-neck.

Given the design of the 5th wheel and its hitch attachment, you might be able to make a partial bed cover, which extends -- at least -- to the hitch point.

Right- the hitch mechanisms are different. But they both go to the center of the pickup box and they'd both be dealt with in identical or at least similar fashion from the standpoint of bedcovers and tailgates or whatever.

Anyway, back to OP's question, seems to me a lot of interaction there and I wouldn't want to make any bold predictions, but I'm pretty sure the "rolling wave" thing that naked pickups have going in the box wouldn't be the case here at all. Seems intuitive that a bed cover would help...

I've seen guys with older hitches that have hatches in their tonneau covers.
I would be afraid with the newer full floating hitches the side movement would crush a hard tonneau.
The big boys use cab deflectors top and sides.
My dad and I have found a properly angled, full width, roof deflector to help at highway speeds.
It may be keeping air from the top from going into the bed.
The air coming from the sides needs to be addressed as well.

Thanks for the comments. I asked something similar on an RV forum which I frequent. Someone pointed out this hitch.
http://www.youtube.com/watch?v=exQGJx_9C3s

It is similar to what I was imagining. Mine would have been taller. However towards the end of the video we can see the problem with a bed cover is really the hardware on the trailer side. The pinbox and pin are too far down below the trailer. In conventional use, the flush lower surface of the trailer in the hitch area is about 6-7" above the pickup bed rails. My idea would require that the existing pinbox be reengineered from the frame down, not just replaced with a short gooseneck hitch.

Interesting. I would think that would help too. It's a sore subject on the RV forum, because 99% of those who have experience or opinion on deflectors say they did/do not help. I look forward to Skyking's test too.