I have been in the same situation and as suggested above, I used a van. However, just check first, as the place I was at specifically excluded the parking of commercial vehicles in the property grounds. I knew this before I moved in, and I had a VW camper van at the time anyway and checked that would be ok – they allowed it as it was not “commercial”. So for me that solved the issue.
The problem, though is then one of security as vans can be easily broken into (especially old VW ones, but shush don’t tell anyone!) – and my camper van was with glass windows so people could see my bike when I forgot to close the curtains. So I bolted (and then had the bolts welded over) a big metal bar from the original load fixing place and made sure the bike was locked inside and to the bar in the van, the van was alarmed and also disabled.
Good thing was I could put bike in there when it was wet/dirty and not have to carry it through the communal areas. Also it meant that panniers and extra bike clothing , spares and tools were all with the bike and to hand.
I think that SORN has changed as of last December - I understand that once you (not a previous owner) has declared SORN then it is now continuous and you dont need to do it again...but its free anyway, so once you have the vehicle there, then you just do a simple SORN application (can be done on-line). Check it out though, wasnt a problem when I did it.
Van became a useful place for other things too though!