@ffm2 I assume Arch has the latest Blender which deprecated (removed?) the DAE import and export because they no longer wanna support this. This means 0 A.D. is probably the last big open source project to use the Collada format. I haven't checked if the settings allows you to restore it;
Doing a bit of 3D printing myself, NIFA is right, unless you get a way to get the normal map details from the textures, your models will look very bland, and they clearly are not meant for printing, because of their non manifold nature.