Printer has informed me of need to have a 1/8" gutter area on the inside of each page.
Reading that the forth time, I would translate that literally as 1/8" white space, all four sides. (Inside the page being the key word)
If this is correct, for the whole document...
Go to the Master Page(s). Make sure both are selected from the Pages Panel preview.
Layout > Margins and Columns - .125in for Top, Bottom, Inside (or left), Outside (or right)
All design elements; type, graphics, everything, keep it within the (Purple) Margins shown on the Pages