I have a 14' otter and I run the 36x16x16 dry box from nrs in the stern end and the frontier play 38x18x13 kitchen box up in the bow end of my frame.
Having both sizes I my advice is to consider the size of the items you want to keep in the dry boxes.
The kitchen box is at the bow end and makes unloading it at camp easier.
My cooler and the kitchen box are both 18" tall and sit at the same height. I usually put a paco pad over the front to make a giant seat to bridge the narrower 13" box width.