I need to prepare this object for 3D printing. I have no idea how to create the surface closing it from the bottom. Could someone give me a tip on this? I’ve been trying to do in very sketchy ways, it has not worked well.
It’s not straight so cutting with a surface has not worked well.
you can duplicate the edges which you want to close all the way around, join them together if you have it broken up in several parts but leave two segments maybe at the long sides and use edge surface that will close it. but you still would have to make this solid meaning offset surface as written before. and you then still would create an insufficient object meaning that just closing it will create nonmanifold geometry due to the surface inside which you just cover up.
or you are trying to create a complete different part and since we dont know how that shall look its a bit difficult to help. the very lets say economical way of describing your part is also not helpful in letting others understand what you need