It appears that squish preserves texture coordinates for meshes. So if meshes are ok then you can use these steps:
- Join all the surfaces together (to make next step easier)
- Use _Bake command to incorporate the decals into texture. Pick high enough resolution.
- Use _ExtractRenderMesh to convert to mesh (squish will preserve texture coordinates on meshes)
- Hide the polysurface
- Use _Squish to unroll the mesh. Set SplitSeams=Yes to unroll each tube section separately.
- Use _Explode on the unrolled mesh to separate the parts.