For Indonesia, I am pretty sure they don't need any "Protector" in SCS, be that the US or China, it's of best interest for Indonesian to look over to the interest of Indonesia, and stay away from either China or US.
But the ground reality is, who Indonesia is going to trust when it come down to a battle of control over SCS? For Indonesia, US is 7,000 miles away, what they want does not affect what Indonesia in such great scale, but to Indonesia, China is just a few hundred miles away, everything Chinese do have a direct effect of their neighbour.
And from what we seen over the last 2 years, I don't think China is giving out a positive image to its neighbour.
It's very easy to keep US out of SCS, by keeping China out of SCS too.