For the most part, the back of both the P182 and P190 are the same. Placement of the ATX backplate and expansion slots are the exact same for both cases. Cooling wise, a 120mm fan, specifically the Antec Tricool, is used to blow air out of the cases. The fan slots are covered with the a honeycomb pattern grille, standard in many Antec cases. For those with watercooling, two rubber ports allow for tubing to be passed through without any case modifications.
On the bottom of the cases are spaces for the power supplies. The P182 allows you to install one ATX power supply, and the P190 includes two power supplies (comprising the Antec Neolink 1200). The P182's power supply is oriented horizontally (most common). The P190, with two supplies has them both oriented standing vertically. Although the P190 comes with stock power supplies installed, you can remove them and install your own power supply (or supplies) to the case, as standard mounting holes are available for use. There is no plate provided to cover the other hole if only one power supply is used.
A simple fan control module can be found at the top of the back of both the P182 and P190. The fan control is similar to the one attached to Antec Tricool fans, a switch with High-Medium-Low settings. The difference is that the module for the P182 controls two fans (back and top), and the module for the P190 controls three fans (back and two on the top). There is an interesting typo on the P190 controls, reading RERA instead of REAR for one of the fans.