Be sure you have a really well-insulating pad--or pads--underneath! Maybe a CCF pad beneath the Prolite Plus. That can make all the difference between shivering most of the night and being cozy warm!

With the extra clothing, liners, etc. with the sleeping bag, just make sure you don't compress the bag's insulation, which will reduce the warmth and thus offset what you've added. Another possibility: if you have or can borrow a summer weight sleeping bag, you could drape it over the top of your 30* bag.