In reply to your insurance question:
Although only a RCD CAT D hull, the 2.7 Airdeck is a well respected tender to bigger boats that often have to use outlying moorings, so ventures into the sea are commonplace.
I don't think you would have an issue, unless the policy stated that only a CAT C boat or better could be used in the sea.
I insured a 3.2m SIB last year with Covermyboat, as they have a specific Small Inflatable policy for boats under 11ft. There was nothing in the policy wording to suggest it couldn't be used in open water.