That's a real help, thanks R o T. I'm embarrassed that I hadn't found the links to the earlier threads myself; I was on holiday when those discussions took place and failed to spot their relevance.
I want the BU for mobility so will persevere with that for a while. Looking at an external SCSI-2 HP model which, with a SCSI card, is pennies many! And there is still the problem of power. Needs more thought and an internal IDE drive may be best in the end.
Recent holiday meant taking power supplies for Notebook, 'phone recharger, camera battery recharger & wireless. Maximum needed at one time was two. But you have to use the specific charger for each piece of kit otherwise the guarantees go out of the window. The price of geekdom!