You extract skin surface of a body part or the whole body the same way. You may need to adjust some parameters, such as neighborhood size.
That should be fine, as long as you only have a handful of air pockets to fill. If there are too many then it may be better to use Grow from seeds effect with two segments (“body” and “outside”). You can start with a few very bold strokes and make adjustments as needed.
If you don’t need small details then you may resample the input volume before you start segmenting, using Crop volume module. If you just want to remove points from the generated surface mesh then you can decimate the closed surface representation as described in this post: Size of STL/OBJ files - too many triangles - #2 by cpinter.