It says you can target these weapons separately like a chariot or wagon, but I cannot find the MTN/RTN for them. Since they don't have a move, martial, or defense value it's not intuitive to calculate it either.
I treat all of these non-listed Characteristics as being 0. Any attack against Heavy Weapons, therefore, automatically hits and resolves against an XTN of 0. The weapon cannot make any attacks on its own, and may only fire if crewed by an appropriate number of attendees.
The only way to increase the XTN of the Heavy Weapon would be via things like cover, high ground, etc.
I treat all of these non-listed Characteristics as being 0. Any attack against Heavy Weapons, therefore, automatically hits and resolves against an XTN of 0. The weapon cannot make any attacks on its own, and may only fire if crewed by an appropriate number of attendees.
The only way to increase the XTN of the Heavy Weapon would be via things like cover, high ground, etc.