Jerome,

Once 'not-part-of' the service equipment, yes, the neutrals need to be isolated from ground.

And 4 feet away is 'not-part-of' the service equipment. Even if you had a meter, then a main disconnect (the service equipment), then right next to it a panel, that panel would not be part of the service equipment.

In your case, the 400 amp main is the service equipment. Once outside that enclosure, everything else is 'not-part-of' the service equipment.