Pretty much any euro spec skelly will keep you under/at 4m. Nothing special needed. Just proper kit.
Why do we run containers 2ft higher then our european cousins, probably just because we can. Fuel savings would be interesting over a ten year trailer life.
If i ever did containers, which as everyone says the rates are ■■■■ i wont, itd be with a d-tec-broshuis trumbone spec skelly at 4m.