Welcome to our forum.
I agree with Chas....Concrete is the way to go.So many people spend thousands on a new spa then run to save a few pennies on the foundation.It's like buying a great home, but telling the builder to try to cut corners on the foundation.I got mine poured for about $500. I dont know how much these "pads" are, but the concrete is well worth the few extra dollars.
How many people that had patios or slabs poured or built had done Zep's setup and had the wiring ported through the slab or patio vice just running in along the side of the slab?
i didn't really "coordinate" with anyonethe morning the concrete guy was to arrivei just ran to Home Depotbought a piece of PVC with a 90 degree curvetold the guy to place it in the back corner about 6 inches in..of the slab he poured& have it stick out from the side of the slab just below ground levelhe said "no problem"came home from work and it was donewhen electrician arrived a week later...it was there for him