It will be fine so long as its off a public road.
With regards the tax though, it's a tricky one, on one hand the government tell you that you must tax it prior to the due date, but on the other hand they tell you that you can keep it off the road for upto 14 days before declaring SORN. Im not sure if the latter rule does not apply if the vehicle has no tax.
If you tax it in 14 days time, you will still pay for this month (it's not pro-rated) so you may as well just tax it. If you want to tax it for next month onwards (to stop the government ripping you off) you must declare it as SORN, and then tax it from the 29th December onwards, although you won't legally be able to drive it until the 1st December (and the post office will be reluctant to tax it even on the 29th).
If you tax it online, you can drive on the tax disc for upto 5 days before your new tax disc is recieved. So you would be taxed immediately.