You can use box mapping projection for textures, but you can unwrap a medium-res mesh as well, provided that you set up correct edge seams, I often do it.
For easy selecting the the seams you can make use of Shortest Path Selection in Edge mode (Ctrl + click-select) or, in Face or Vertex mode you can select a large portion of the mesh and then ‘Select Boundary Loop’ from the Select menu.
Thanks sourvinos. The thing is that Most of the time I dont want to unwrap and make a lowpoly mesh just to paint a bit. Vertex colors are a bit hard for me I prefer texture paint by UV if you ask me.
I think maybe the best is to make a low poly version using shrinkwrap just to get away. Thanks.