Great project so far! Just wanted to throw you my 2 cents from personal experience with my setup...
That PSU may not be adequate for a single PSU setup to run 2 jrk boards at once. 12v x 30A = 360 W, Not knowing what your motors will
draw under load, it's hard to really answer your query with a definite answer. But this math can be used as a guide.
I run 2 boards with 1 power supply myself, but I'm only moving a seat and H-shifter attached , and it's mounted with a U-Joint directly underneath. So,
there is very little load added to the motors from anyone sitting, and not much more added during motion.
It took me a good while to get the PID set correctly before it would be stable enough to handle various size/weight people on it without having the
PSU cut off due to AMP spikes out of range. Mainly from the fast direction changes.
So the amp spike draw for both motors are no where near what your setup will experience having to move the entire platform under load. The only
sure way to know what kind of PSU setup you require would be to test your motors under load with a car battery and AMP meter. I believe
the amp draw is doubled during immediate change of motor direction giving the massive spikes under load. Quick and easy to
test. Once you know what AMP draw you have for how much weight, just double it up for 2 motors, and get a PSU with 20% more power than what your
total MAX would be. Which I think would be cheaper than 2 separate power supplies. Unless your power requirement is something outrages due to spikes,
in which case, an inline car battery may be an alternate option. I've seen that solution used by many different wiper mover projects as well.
This is my simplified version of the math. Anyone with more technical expertise is welcome to explain it with more detail.
Hope this bit of info is of some use to you...