How about heavy duty 5w tail lamps? Halfords sell them (expensive, but if they last longer...)

If it's destroying number plate lamp bulbs, even LED ones, the most likely cause is a duff earth somewhere. If filament bulbs fail with a heavily blackened appearence to their envelopes, this is disgnostic. Check for a seperate earth lead from the lamp unit screwed to the bodywork in that area. If none, it'll be earthing back through the unit to the body, so remove the lamp unit and ensure there's good contact there (or solder an earth wire onto it and attach it to the body somewhere).

The Berlingo's got a tail door, so the earth lead probably runs back through a flexible boot to attach to the shell somewhere in the rear of the vehicle. If so, check the wiring inside the flexible boot. Fatigue breakage in the conductors of the wire or a "chewed" lead, due to entrapment, in this area is all too common on many vehicles.