Seems that nobody is reading carefully the thread and the last post of the OP. He says the place is "Castello di Casiglio" that is not actually located in Como, but in Erba, a small town, not on the lake, about 15 km east of Como (half way between Como and Lecco). So the train option is not praticable. He says also that with his tentative schedule he has a flight to VRN leaving from LGW, after an easy conenction from JER, on the other side reaching MXP or LIN requires a transfer to LHR. Everybody knows that MXP or LIN are much closer to Como and the Lake region than VRN, but in this case the OP has the transfer LGW-LHR and I can suppose at least 2.5 hours of trasfer time, considering baggage pick up at LGW, check-in at LHR and security checks. In my opinion this is a bigger hassle than one more hour of easy driving time on an highway.
Arriving from MXP you should add about 30 minutes of small roads to reach the location, so I can suppose at least 1,5 hours of travel time. Arriving from VRN you may leave the highway at Bergamo and then proceed to Lecco and Erba, avoiding in this case the peak hours traffic around Milano. VRN airport is very close to the highway (the runway ends on the side of the highway) and I did several times VRN to Como via A4 and A8 higways in about 2-2.5 hours (210 km). Considering the OP is not familiar with the right hand side driving in Italy, I can suppose he can drive the 180 km from VRN to Erba in less than 3 hours (that is a 60 km/h average speed).
With all the details reported by the OP, considering his flights schedule, at the moment VRN is still the best option.