Personally, I'd select the undermount tub and then use a solid (3D polygon) to make the deck. That way, you can make the hole in the deck suit the tub shape regardless of the tub you actually use on the drawing.
A lot depends on what shape the undermount tub is ... and whether or not you have a symbol that's close to it.
You must draw the solid with the hole included in the shape and then close it. You can't draw a shape and add a hole.
You can make the skirt from a solid the same way. Again depending on the symbol you may be able to make the original solid deep enough to form the skirt too.
NOTE: A couple of the Kohler tubs in the Manufacturers Library come in undermount styles.
Version 7 to Version 2016 in one step is quite a jump. You may be saying "WOW" for quite a few days ....