The mammoth already has a platform saddle in ark mobile but you have to buy the engram with real money. Click the up arrow if you want to help convince wildcard to add it into all versions of ark fully including ark mobile for free!!! Help start the petition revolution!!!!
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!