So I was struggling with a Otomo-convert shimazu Coop campaign, and I decided to use that tactic I saw a while ago of just raiding through everything not caring about rebels and avoiding the enemy army....
Start of the war: 20k reserve fund, 2000 per turn
End: 72k reserve fund; 4000 per turn

My enemy didn't loose much military but they lost almost all of their land to rebels after I was done raiding it all and I took them from affluent to meagre.
Now just have to use the same strategy again on 3 more massive clans :C