On my
insurance document (Safeguard) it clearly states that the insured vehicle must be taxed at all times for it to remain insured, there was no reference to SORN. So I asked them (Safeguard) the question the other week, and yes, the vehicle is still insured whilst under SORN, I have that in writing from them. However, I only asked if this was the case for when it is parked in its secure CasSoa Gold compound (which is part of a campsite as it happens). So if it were to be parked elsewhere I would advise you to check with your insurer.
I am never going to be on a campsite in Benidorm for 3 months, so that part of the question doesn't really apply to me, but I cannot see how it would matter a jot to an
insurance company whether a vehicle is taxed or SORN'd - so long as it is NOT being used on a public highway, here in the UK or abroad whilst it is under SORN. And I cannot accept that your personal pitch on a campsite with a entrance barrier on the Costa del Sol, is a public highway.
One thing is for certain though is the fact that you will definitely NOT be insured if you have no MOT.