1)
Did David leave any Kohanim with the Aron?
2.
Malbim: Yes - "u'Vnayahu v'Yachazi'el ha'Kohanim ba'Chatzotzeros Tamid Lifnei Aron" (6).
2)
What do we learn from "ha'Bamah Asher b'Giv'on"?
1.
Redak (37): The Mishkan was in Giv'on, and a Bamah Gedolah. Only Kohanim may offer on it. There was a Bamah Ketanah in front of the Aron - Zarim offered Olos on it.


