Yes,Mildenhall was the airhead for Feltwell and it's four sites - Shepherds Grove,Tuddenham,Mepal and North Pickenham. I never saw one being off-loaded either as they were all in situ when I was posted to Feltwell in May 1960.I saw plenty being loaded for return to the USA and I also saw plenty on the local roads in Norfolk/Suffolk.
I can't remember where I got this photo from but USAF Studebakers were used to pull the missile trailers in the late 50s until RAF Leyland Hippos were used.
The total length was 90ft including the tractor unit and some site access roads had to be altered to accomodate the vehicles.The trailers had originally rigid rear bogies but were modified in the States into steering axles with two airmen on the back end in contact with the driver.