Hi, welcome to the Community! 
Papyrus Author doesn’t have a dedicated feature for setting up trim marks on the page. Let’s see if we can find a workaround!
In this previous topic, the workaround was setting up a page border: Page border or crop marks
Could this work for you as well?
By the way, have you already seen the book template for a 5x8 project with added bleeds for print? You can find it by going “File” → “New Project”, and selecting “5x8 (+bleed)”.
Let me know how it goes!