I mention shopping carts because the cargo and trailer rules aren't great either. Improving them would probably negate the need for "trains" to be constructed as a separate unit type.
Can't fault the writers for having fun devising new systems, nor the fans for having fun exploring and testing them; but... look, the point of "support vehicles" is to have archaic tanks for 'Mechs to shoot at and soft civilian vehicles for RPG characters to shoot at, and... isn't that handled by making armor less effective per ton? Are separate "penetration" and "BAR" values really needed, or can that be handled with range, damage and armor factor?