Trailers tend to be the forgotten part of trucking so there is little documented. Dennis Brooks in his monograph records the transition from 41' to 45' as 1992. In your period McGrath/Freighter and others ere active however Maxicube/Maxitrans came to dominate the field. The transition from bogie to triaxle was also happening. Air bags while very popular have never actually replaced conventional springs. Refrigerated trailers don't have a chassis as such - they tend to be a firbreglass composite box sat on a sub-chassis on the rear and a tow plate attached to the front. Due to the lack of conventional chassis they don't get on well with heavy forklifts and have been known to fold in half if abused.
As mammoth stated 45' trailers became legal in 1992. Overall length was still 17.5M though.
Mid 90's overall length limits were relaxed to 19M, & from 23M to 25m for B doubles...
There were a few 22 pallet (45') trailers sneaking around Prior to '92 though..
You often see these trailers used as storage on farms ,as they are lovely and cool inside on a hot day......they generally only last about 5 years in service ,before fibreglass rot,cracking,and problems with the steel subframes shows up.....they sell for a couple of hundred sometimes at auction.