I've only heard of two houses, which
@Lilly b mentioned have been discussed at length on earlier threads. His main residence - likely from 2000 until he went to prison in 2006 - was the farmhouse outside PDL. He is also reported to have stayed at the School House in Monte Judea - IIRC he looked after this house for an older expat lady from time to time.
IMO, if a door was knocked on, it would have been the farmhouse because this was probably the only residence he listed for phone and utility bills.
It's very unlikely they knocked on the MJ house because I don't think he ever actually lived there and that the police knocked on a van door is a stupid suggestion - how did they locate it, was it even registered to CB at the time?