I would second going to Multihull World who can put you in touch with a specialist multihull surveyor
. They could also act as a buyers broker
, which as I understand it means that their fee comes from sharing with the seller's broker
, if there is one.
They are also based at Thronham Marina nr Emsworth, https://www.thornhammarina.com/
and usually have berths but useable only a few hours/tide. There are quite a few tidal marinas
around Portsmouth, Fareham Marina and Wicormarine in Portsmouth Harbour itself.
If you are prepared to have a non alongside berth, there are a lot of tidal and deepwater moorings in Chichester, Langstone and Portsmouth harbours. Also, some sailing clubs do have moorings. We kept out 10m cat on atidal mooring
in Langstone harbour for 10 years, just grit your teeth and think of the 100s of £ you save every time you get wet and muddy to get to your boat!
For insurance, Try Pantaenius https://www.pantaenius.com/uk-en/
, Coleman Marine https://colemanmarine.co.uk/
both of whom I have used without issues.