I'd not go OTT on "insulation" straight away... When flying, the general air flow will prevent any heat build up. The "problem" we find is on the ground after flight, when the general heat build up of the engine will warm up the front end of the aircraft - and I am not sure insulation will make much difference?
Thoughts - not an issue unless you have something in the baggage bay that is heat sensitive. We have a smoke tank there, and that is an issue - heat makes the viscosity got down so flow rate up. It is not a problem on a long transit, it is a problem with a pre-position flight, when the time on the ground then heats up the oil.
You could reduce this by the usual trick of opening the oil door, the baggage door, or just removing the heat sensitive luggage (food?!) soon after shutdown.