I am going to pull the carpet and seats and and paint the whole inside of my 87 sammy with chassis saver. Would the quart cover it or would i need a whole gallon? Sorry i'm a newb.

You will need more than a single quart of CS, probably 1 and a half quarts to 2 quarts to fully do the job. What I would do is get 1 quart of silver as the "primer" coat and then follow with either of the black's or the grey CS.

I used CS on a bunch of projects and always apply MonstaLiner overtop of the ChassisSaver when used for the interior.