Load will be dependent on a lot of factors:
Sail material (nylon absorbs some loads)
Tenderness or stiffness of boat (this is why cat sails
are so heavily loaded - the boat doesn't heel)
You mentioned your spinnaker is 108m and that you expect the gennaker to be smaller which is true. If we were selecting a foil-less furler
for the boat we'd probably be looking at something with at least 3500lb working load.
You may want to consult a rigger for advice on which fitting to procure.