On the raft build a 3x3 foundation with 3 walls high and a ramp going up into the raft. Go to the winter area youll find Mammoths there. Get it into the raft. Once in the raft shoot it with tranq arrows. Starve it and then feed. Kibble is 80times its food.
Build a raft with about 9 or so foundations/ ceiling and put Walls on the perimeter and ramps in the front and put large storage boxes along the walls and go to the swamp with a buddy and just sit on the mammoth on the front of the raft and swing away. Best wood/thatch/shroom farm ever
For wood, put on raft with large flat deck. You and your buddy drive through the swamp, swinging away. Raft has no weight restrictions. ENDLESS wood, thatch and mushrooms. Careful not to push off, go slow. It adds up fast, regularly took home 10,000+lbs of materials.
As to a posed of the Giant Beaver, this creature has a bonus where wood is x0.25 it's normal weight, combined with its large carry weight it's the best option for gathering wood. Ps: Giant beaver ' s mod. is x0.5!