What is "Musach ha'Shabbos"?
Rashi: It is a roof made for shade, to sit under it in the Azarah on Shabbos. Radak - the root is Yasach, related to Sechach; both of these roots are the same matter.
Radak citing Targum Yonasan: Tikus Shabsa; some texts say Yas Tekes Madbecha d'Shabsa. It is a structure to take shelter under it. It is called of Shabbos, because it was made for the leaving [Malbim - and entering 1 ] Mishmar. They did not have Avodah that day, and sat there until the day ended. The verse does not say what he did to it; it seems that he destroyed it.
Also the entering Mishmar did not have so much Avodah - on Shabbos we offer only two Temidim and two Musafim, but no voluntary Korbanos! (PF)
What is "Mevo ha'Melech"?
Rashi: It is the path he would go on from his house to Beis Hashem from the outside.
Radak: It is the entrance to his house, which used to be external. He diverted the entrance to be via Beis Hashem, to be sheltered from Melech Ashur (lest Melech Ashur want to kill him). Malbim - he made Beis Hashem his path, so others would not leave and enter there. Then they extinguished the Neros and ceased the Avodah, like it says in Divrei ha'Yamim II, 29:7. The Navi was concise here; Achaz' abominations are detailed there.
