one thing you might also want to do, because i restrict the zoom levels between 12 and 17 (12, 13, 14 is the landranger series, and 15, 16, 17 is the explorer series), and because by default mobac starts with a map of the world (with germany in the center) but limits the zoom level to the minimum for the zoom level of the map source you’re picking, you may want to pan-around with another map source (that lets you have a wider view) and draw your bounding box first before switching to this one. otherwise you’ll end up getting bing maps of germany that you can’t zoom out of (and i don’t see an obvious way to pan around, let’s just say mobac doesn’t seem to have a very well designed interface)
or you could just change my xml’s minzoom to lower number too 🙂 i just prefer to restrict my xml’s minzoom to the zoom levels that actually show OS maps (as zoomlevel 11 and lower will show you regular bing maps), since i also wrote a script to create a mobac profile for each of the actual bounding boxes of each of the official explorer/landranger maps, as drawn here: http://anonym.to/?http://www.ordnancesurvey.co.uk/shop/mapsheetfinder.html