mm well looks like there's no fudge around, but when you guys undoubtedly try to beat the Death Toll campaign on expert, the boathouse finale, the strategy that worked best for us was as follows.
Stock up on all your supplies and shit, get the extra stuff from the cabin off to the side of the boat house. Look around for gas cans and set one up on the entrance to the dock. If the game is nice and you get two, put the other one on the stairs of the dock at the back or somewhere out of the way so you don't accidentally shoot it. 2 people get pipe bombs, 2 people get molotovs. Once it comes time to call the boat, have everyone stand on top of the dock pillars, the two outermost ones, so you can all melee each other in case of hunter pouncing.
2 assault rifles, 1 shotty, 1 hunting rifle. Hunting rifle's job is to take out any specials like smokers and boomers etc. x2 Assaults guard the left and sometimes center of the bridge, assisting the hunter if he gets snared and also taking out zombies at medium range before they reach the dock. Shotty covers center and takes care of anything that gets too close to the survivors. When standing on the pillars, the zombie AI fails or something and mainly all try to climb up the left side of the dock while a few run down the center. This funnels them very easily.
After the zombie waves, the first tank comes. 1 of the molotovers ignites the tank and runs laps around the dock so every one else can shoot the tank as it chases him. If target switches, that person runs laps.
As soon as the tank goes down everyone runs for the boathouse to grab ammo and more nades. As you all run back to the dock after restocking, a pipebomb is throw to make getting back to the dock easy.
Repeat the previous strategy for more waves of zombies, and a second tank. If for whatever reason you fall off the dock, simply stand in the water on the left side and help from there until there is a break in the horde wave and you can get back up.
Once you beat the second tank, the boat will show up. DO NOT jump on the boat until it stops completely. We failed the mission once because we jumped for the boat while it was still moving and it killed us all.