I believe this may be a hunter & troll proof base!
Construct the stairs using a wood foundation placed below water level. This will enable player to fill water canteens from the bottom of the first ladder. You are on the lake & have all the water & kelp that you may need. Then attach a wall to this foundation and place the stairs. The stairs meet the upper level in the middle. When stairs reach your desired height, you just place wood ceilings out from the stairs to create the upper level. Move the foundation & the wall to the next level up and repeat till you get to at least 3 or more levels high, the higher the better (this will minimize damage to upper level caused by grenades). Hunters cannot climb the stairs but may throw grenades which may damage the bottom stairs. Trolls are blocked by 3 doors at the top level. I doubt whether any troll will break through all 3 doors. More doors can be added to top level to deter trolls.