Sorry about not responding ASAP.. (I forgot to respond) yes you can add another SOLAR charge controller to your system. It can be either an MPPT or PWM. I am not sure, but check to see if your current controller has a primary/secondary option. The one feature you may lose is if you have a battery temp sensor, as it will not be able to alter the second controllers output should the battery reach its high end charging temperature. Can you purchase a 60 amp and sell your 45 amp on eBay, to get some of the money back?
Don
We just arrived at the BaldMountain RV Resort in Hiawassee GA, in the BlueRidge Mountains, soooo much cooler than FL!