Mud Flaps vs 5th Wheel Vortex

This question feels a little tinfoil-hat-ish, but…

We’ve been towing a high profile 5er for years and I’m pretty good about strapping down things in the bed because the vortex in the truck bed will blow things around and even suck them out of the truck bed.

We recently towed a shorter 5er with a lower nose and the vortex was more extreme. While part of me doesn’t care since my load is secured, the different air dynamics are driving one of my dogs insane and she’s visibly distressed while we drive.

I’m looking for ways to reduce the vortex and I overheard someone mention mud flaps as a cure but I couldn’t ask them for more info.

Has anyone here heard anything to support this? Or does anyone have any ideas?

My only other idea is to wrap a few straps around my tailgate to hold down the plastic rail cap, because I can see it flutter while we drive. I can’t think of anything else that would be creating a sound that’s driving one of our dogs insane.