You should be ok if you use CH1 for one and CH4 for the other. You would have to be careful with what you atttach to the remaining outlets. If you have 2 PC4's you can put one heater on CH1 or CH4 of one PC4 and the other heater on CH1 or CH4 of the other PC4. Just remember that The closer to the current limit the higher chance of a failure. Make sure you have a backup temp control on each heater set a couple degrees above your setting on the RKL. Relays can fail in the on or off state. Also they did have a PC1 that had single control of 2 outlets at 15 amps total. You may be able to find one of those for sale. If you have a RKL it has 4 module limit.