I think what I'd do is to remove the existing gully, and see if there is any obvious issue with that causing the repeat blockages. If not, then get the outgoing drain surveyed with a Camera and see what's going on there, and decide from there what is the best plan going forward.
It may only need a good clean, in which case, once that is done, fit an Osma Bottle Gully with screw down lid, waste can connect via one of the side bosses, and system is then sealed, but access available in future if required. Floor covering can go over the top to disguise it's presence.