Raised bed 17'x3' by 30" high. Mortar or Locktite or nothing for the bed (caps will be glued)?

Thank you for the question. If you are using landscape blocks, then typically these are dry stacks to allow for movement of the bed itself. This is not to say you cannot use Loctite PL 500 Landscape Block Construction Adhesive, to help hold the rows together, understanding in this situation bed walls may move, especially if you are in an area subject to freeze-thaw conditions. If permanency is what you are looking for then mortar is the preferred method.