If your cabinet is truly enclosed you will have nothing more than a nice convection oven. So get out grandmas cookie recipe and enjoy. You must find a way to vent out the hot air, and must provide a way for it to enter as well. This is usually a bigger issue with custom rack face equipment that provides a nice seal around the face of the equipment, but in closed door installations it is also a huge issue. Drill some holes! Small and large. Top and bottom. where ever you can, but enough. You needn't go crazy, but you will help your equipment to live a long happy life. And you can skip the cookies. Fans are almost an option when you place the right amount of equipment in the right way with properly routed ventilation. The only must haves arrive when we are using high current equipment. Etc. or very well sealed designs. Remember that an elan Z-fan and others like it need a place to get ands put this moving air... Some units will suck or blow though the face. (insert joke here), but not both.