Things I don't see anymore?

[Red-Rover]

Remember those air foils bolted to trucks to improve aerodynamics when towing? Did they not work or do these plastic nose covers do a better job?
Remember those roll out awning material covers installed over the slides? Don't see those anymore because??? Too expensive? no longer offer a benefit?
Just wondering out loud here, if these things worked 15 years ago should we not have them today?

[Bill1374]

The air diverters never mounted close enough to the trailer to be very effective. They did move the bug splatter pattern, but from my reading, had no effect on mileage.
I've had slide toppers on my fifths and mhs for a long time. I rate them very highly.

[downtheroad]

Do you mean something like this? (not mine).

[JIMNLIN]

Air foils ??

Nose covers ??
Can you be more specific