With what you are asking for I would suspect you will need to have the cover custom made. When we decided to have a Kilt manufactured (I wouldn't put a skirt on my "handsome" 40 foot 5er) Hired a company out of Boise, ID with a mobile tech who drove up to SE Washington and he spent two solid days in the winter cold manufacturing and fitting the custom Kilt. Made a big difference in temps under the 5'er. Within 20 mins the airspace under the trailer was 10 degs warmer then the outside temp.
2006 F-550, Crew cab, 4x4 w/factory bed getting 12 mpg @ 50,000 miles
2006 Lance 1191
2006 Wells Cargo 14' Cycle Wagon
2017 Grand Design 5th wheel with EezTire TPMS
2017 F-450 4x4 crew cab King Ranch