One thing that helps is that you do not have to unwrap the entire model in some cases. Consider if you want to map a texture image on 1 face of a cube. Assign the face you want to to unwrap a white material. Create a new material and assign it to the remaining faces.
Select the face you want to unwrap, unwrap, then in the UV image editor open the texture you want to use for that face.
While that face is still selected, open up a new texture slot for it, in panel to far right. With its material also being selected, open up the same image you did earlier, change its mapping coordinates to UV. Under Map, select UV map. Now that faces material has a UV mapped texture applied to it.
This works with several faces also, as long as these faces have the same white material. Reason to use white is that other diffuse colors will tint your image that color in printing. Interesting point you can have several materials the same diffuse color, which will not tint the uv image textures applied to them.
If you want to hollow out out a model, with no problems from UV's just assign the hollow area a material that has not been UV mapped.