IO - I think the insurance issue is a bit of a red herring - the safe option is to copy the correspondence on which you rely to the insurance company and ask them if they are satisfied that the practise you propose will not invalidate your policy - if they agree it will not (in writing) all will be well.
For example while off airport landings are not illegal as such there are clearly a raft of considerations so I wrote and asked if off airport landings would be covered and whether any specific restrictions would apply.