Ah! Sorry for the slow response.

They don't get the boat out -- the boat casts Astral Projection on the PCs, after which they ride its astral double through the Gates of the Duat on their way to the Halls of Amenti.

If they want to take the boat out later, the entire thing disassembles. It doesn't use caulk or nails; the entire thing is held together entirely with ropes, just like the real-world one found at Pharoah Khufu's pyramid.