So, I have a bottom item and a few chest items that have arms and legs that pose differently than the base (ie arms up/at sides or legs crossed) and I don't know how to wear them without the original base peaking underneath. Is there a new technique to use or something I'm missing?

In the wardrobe, click over to the Base tab, and there you should see toggles that will hide your HA's limbs.

Ahh gotcha! Thank you much!!!