the easiest way is stock up on a lot of smoked meat and clay water bottles. then just stand in your hut to guard you from the sun rays. then just keep your character full and hydradeted for ten days without sleeping. you do not have to be at sea for it to work. you just cant sleep for ten days. try to make sure your at full health, food, water before you start… its how i did it. i put my controler down and just came back and checked about every ten minutes to see if needed food or water. kept doing this until the trophy popped. took awhile. i just kept checking notifications every so often till it told me i had achieved trophy. i would suggest crates full of meat and water at your feet so you can eat and drink without moving your character much to avoid more exaustion. good luck.