I don't know where the entrances are for the Tiger River spas (for Sundance Maxxus, they are on either side corner of the end where the controls are, for example). But, as an electrical engineer and someone that knows something about construction, I'd advise again putting the spa on top of the power conduit/cable. You never know when, down the road, ten years from now, moles or whatever, will chomp away at the cable and make you *have* to access that cable or replace it elsewhere. [Of course, they be *dead* moles after the fact!]
Your options will be to move the spa to access the buried cable (bad) or abandon that buried cable, and run a new one 'somewhere else' to replace it. Either isn't a good answer; if putting it somewhere else was good, you would have done so now.
I'd run the original cable somehow so it's not obstructed by having a structure on top of it. Now, you may last many years with no problems, but that's the conservative engineer in me saying leave possible access to it.
Even putting it under the edge of a concrete slab/pad isn't too bad since you can jackhammer that up and replace it. Under the whole spa? That's different, unless you are aware you may have to abandon the whole run.
Or am I all wet in this case?