The problem with any of this stuff is payback.
If you are putting aero gadgets on your trailer is like putting lipstick on a pig.
A trailer is super dirty aero wise. If you fix one thing there are 50 more things you can't fix. The wings we saw in the 70's were a prime example. How many wings do you see anymore? There is a reason.
This Caterpillar study show what is big in fuel savings As you can see, the way you drive your rid has the biggest fuel savings. Up to 20%. That's a very large savings. Route can be up to a 20% savings too. Between route and how you drive you can save a lot of fuel.
If you want to save fuel the best way is to slow down and drive sensible and pick the best route.