My primary concern would be keeping the heat even between the 3 sections. As to 2 110v elements, you could, but you need to also be thinking about what electrical power is available where you will use the smoker. A 1,500 watt 110v element is pulling around 13.65 amps when on. So two of them is 27.27 amps and would give you 3,000 watts of heat (more heat is better with a larger volume of air column to be heated like in a bigger smoker box). You would need a 30amp RV circuit at your house to make that work. Not many folks have them. If you are going to be running a dedicated outlet specially for the smoker, going 220v would be better. With 110v at 3,000 watts you need a 10 gauge or larger wire. But with 220v you could stay with 12 no problem (actually 14 would work, but bigger is still better and 12 is uber common). If you wanted to run 3 110v elements (1 in each section), then you are looking at 4500 watts if you stay with 1,500 watt elements. You would have to be on 220v at that point, but you could split it into individual 110v legs at the smoker, but you are still looking at at least 10 gauge wiring. Even though the elements will be pulsed by a PID controller and not be on full all the time, the wiring needs to be rated to handle full power all the time for safety.
Have you tried any testing with a single element and the convection fan yet to see what the temp spread is and how even it is between the chambers? I would hate to do a lot of work and find out the airflow between chambers from the fan is not what is needed.