I hope this is the right place to post.
it is probably difficult to have both playing on one campaign map. How about players taking their score to a new coop map where the game rules are optimized for coop play. That way you could take your own armies, fight battles together and do coop missions. Maybe there are recruiting offices for new recruits and special items to buy in the cities. The gained loot, new units or resources could then be brought into your single player save.
I think that would be a good compromise between co-op and a pure single player campaign.
it is probably difficult to have both playing on one campaign map. How about players taking their score to a new coop map where the game rules are optimized for coop play. That way you could take your own armies, fight battles together and do coop missions. Maybe there are recruiting offices for new recruits and special items to buy in the cities. The gained loot, new units or resources could then be brought into your single player save.
I think that would be a good compromise between co-op and a pure single player campaign.