Installing above floor rough in tub

[htech]

I'm new to the forum and installing bathtubs in general and was hoping to get some advice before I screw something up. I bought a Sterling tub and I'm about to install it directly on a concrete slab floor. The floor is off level by about 1/8". This is an above floor rough in tub so it sits on a plastic riser that lifts it up for drain clearance. My question is should I put mortar underneath the tub when installing it? My understanding of mortaring underneath a tub is so the tub sits in the mortar and it conforms to the bottom surface of the tub providing a sort of level "cradle" for it. Is that correct? If so I don't see how I can achieve that with this type tub. I contacted Sterling and they were less than helpful and just said it was my choice to use it or not. Can you guys tell me how you would install it? I just hate doing things the wrong way and regretting not asking someone before I did it. I've attached a couple of pics of the bottom of the tub.

Thanks!

 

[Geofd]

we have installed a handful of those sterling tubs the tub base is very sturdy we did not use anything under this brand...and they are in college dorm rooms some have been in for 10 years some around 5 years..we didn't use that riser it sat right on the floor...so it couldn't hurt were your tub is sitting on that cradle

 

[bbp]

Type S mortar. Extra 20 minutes, no shims,rock solid,retains heat,$8.00 a bag

 

[frodo]

simple and easy to do
2--5 gallon buckets of quikrete
mix it on the loose side, not stiff
dump them on the floor, set the tub over the mud bed
press the tub down and level. as you go
secure tub edge to studs

 

[htech]

Yeah the thing that's definitely throwing me off is the black stand it sits on. I have never seen that before.

 

[htech]

I guess it couldn't hurt underneath the cradle where it meets the floor just to make sure that the feet are fully supported. I just hope that the tub is strong enough not to flex without the whole bottom surface supported by mortar.