The only place to launch a 10 metre RIB is at Newhaven. You need to contact Simpson Marine Telephone : 01273 612612. or Newhaven Marina Tel : 01273 513881
They dont normally launch boats this size so I would speak to them first.
You will need to launch & retrieve near HW due to the slipway angle, the cost is approx £26.
Parking is now much reduced at Newhaven due to new building work.
Shoreham has Lady Bee marina, but due to the slipway angle there is no way that you will manover a 10m trailer into position.
Eco Tourism Rides from Newhaven, East Sussex.