Build a raft. Place fence foundations around it place wooden door ways on top now you can place stone doorways underneath build 3 deep underneath the raft. Snap pillars in the doorways in the back build it 4 pillars deep. Build ceilings underneath it and one outwards facing the front build 2 fence foundations in the front place a dino gate on them and you 've got an mediocre tame box for mantas but bewary they will be able to hit you if you use bug repellant you should be fine.
Tame a kaprosuchos and swim to one of these bad boys and do it's alternate attack it will grab it in it's mouth. walk onto the shore where its safe and have another person feed it while in the gators mouth (if you unmount it drops it) it wont attack or die because it's technically not on the shore.