winch for lift

jus building a new cantilever lift for our boat, want to make it 12v electric but don't know what rating of winch to use, it will have to be the sort you see on rv's, as its not economical to import the ones made for this type of lift from the US
I want to keep it as physically small as possible whilst keepng it safe and don't mind having to use a double pulley system to help with this.
it's a 4000lb lift but is being home built as we cant get them here any more, the pound just too weak.
look forward to any ideas or thoughts.

Many thanks
Dave