I am also based in Jersey. We have a 12 man liferaft for charter work and it is a pain!.
Realistically, look at the furthest offshore you are likely to be, not distance to places, and also weather you are realistically going offshore in??
Jersey St Malo - 8 miles from french or Jersey coast / minquiers
Jersey - Cart / portbail 5 miles Ecrehous in the Middle
Guernsey - 10 miles
Most likely need for a liferaft on a Rib is FIRE!! whether caused by electronics or engines. Also need to think how many people you need the liferaft for.
hope this helps a little