The above suggestions are good but also could consider plastic welding depending on how yours are coming apart. I myself have never had it done it before but have heard it can be done. Im not sure whats all involved or how its done but with a google search you may come across something.
I had the same problem with my 2012 xp. They were cracked on both sides from previous owner. Drilled holes on cracks so it wouldn't spread and covered with vents. Now it has more ventilation. Two birds with one stone. Vents were about $100 for set but I think you can get them cheaper.