Molding difficulties at home (made by gypsum powder and mold gel)

Last whole year, I've searched so many information about molding on web, I find it seems really not that easy to make it at home if I want to create a container body with curve. Actually it's easy to make a mold for object with simple shape, you just need the mold gel and gypsum powder, and then do it as the following steps will be okay.

instruction given by Newlink Resources Limited

You could see the steps above, we need 2 mold blocks for outside mold when the final object is a solid. But since the object is an arc-shaped container, we should need 3 blocks instead. In these situation, difficulties come! Firstly, we don't have the vacuum casting machine at home. Secondly, when we have to make 3 parts of mold, and we must make the mold blocks(part 2 & part 3) by laying down the solid mold horrizontally, I really wonder if we could stick it tightly at the right position with the outside mold part 1? See the situation below, are there anybody got solution for these? I guess people may meet the problems during creating works, hope can join the discussion and make it solve, thank you!

Mold gel information:http://www.shinetsu.com.tw/html/en/html/pdt2.asp?area=65&cat=215&sn=92
http://model.chingb.com/ModelTutor01a.asp