If you need good reference material this is the site to see, they got sleeper measurements, tanker pictures.............http://www.stlouisdumptrucks.com/index.html
I've just bought the Testors Big Rigs Tanker trailer & will try to convert that, seems to be the closest of all the tanker kits out there. Dave from AITM did inform me that he might do a tanker sometime in the future.