These 3-D shapes occur often in math textbooks, and hopefully when they are transcribed consistently the students get used to reading them. It also helps if they have used classroom manipulatives when first learning the various shapes. You are on the right track by using solid lines for the outline and dashed lines for the "invisible" lines. Sometimes in print the basic shape (usually the base) is shaded, or a heavier outline can assist in drawing attention to the basic shape. I always change the orientation so that the 3-D perspective is to the right, with the basic shape parallel to the page rather than skewed. I have attached a 2-page file of several examples you may wish to refer to.
Hope this helps!