It's impractical to drive a Tesla with no trailer that distance, let alone with a trailer. I wouldn't bother with that exercise in driving strategy and fortitude, especially if there are other passengers along whose time is also worthy of consideration.
That said, you'd probably be better off designing a tapered boattail for a single axle trailer than just tossing that on top. Of course, the top of the cover does need to be covered.
I barely notice a decrease in FE on my empty trailer with the sides off, but notice a huge drop in FE with an empty trailer with sides up, but no cover.
Can you get away with something like this instead:
