What is "Beis Ashtaros"?
Radak: It is [the house of] their idolatry. They are idols in the shape of Ashtaros, i.e. flock 1 - "v'Ashteros Tzonecha" (Devarim 28:4). In Divrei ha'Yamim 1 10:10 it says "Beis Eloheihem" - these are the Ashtaros, which were their gods.
How did they hang his body?
Radak: They hung it via nails.
In Divrei ha'Yamim 1 10:10, it says that they inserted his skull in Beis Dagon!
Radak: What is not mentioned here, is mentioned there. They inserted his body in the wall of Beis Shan, and his skull in Beis Dagon. [They could be in different places,] for they cut off his head.
Here it says that only that they inserted his body in the wall of Beis Shan. Below (verse 12) it says that also his sons were inserted in the wall!
Radak: The verse was concise. "Geviyaso" includes his sons' bodies.