In order to keep its shape you could even fill it with expanding foam - just cut large holes between each part, so the foam can expand from one part to the next and then spill out of the bottom - then you just shave it off. And in order to attach the chair and telescope to the base, instead of heating the peg under the chair to squeeze it into the socket, just heat the base so the socket becomes pliable.
I never finished mine as I wanted to find a way to make the base sides completely vertical and not slope and be uneven in some sections - I want it to look machined.