The first time I saw one was at Halton not long after it had arrived in service.....unfortunately, the "somewhat elderly " civilian instructor didn't appreciate my powers of observation ....and his metronomic incantations being disrupted when I informed the class of its presence
Never got work on them in depth only when passing through or night stopping. However, one aspect that did put the size into perspective, for me at least, was the compartment behind the rear px bulkhead..... and the size of the screw jack / box section for the horizontal stab. Took HM Customs up there a couple of times as part of their training and remember being asked if I went up there on a regular basis. I said no, but, equally, nobody would be suspicious if I or any engineers did. HMRC kindly informed me some enterprising souls at AMS ? had worked this one out and decided the box section on the stab would make a convenient storage area for the products of a certain South American country noted for its exports of such.