Deck is off the ground about 2'. It was pretty well covered up on the bottom with skirting, but I removed all that and will replace it with open steps that run the length. There will be pretty airflow under the deck from now on.
The deck faces North. It gets heavy morning and afternoon sun. No shade trees to help it. No water or other features on the deck. Summer tends to be pretty dry here, but it's very moderate compared to the rest of the county. It'll be wet for 8 months and get sun most of the other 4.
Re the planters, they have no bottom. I'm putting right on the ground. I'll take some metal fabric to the bottom to keep animals out. But they'll be free draining. Good idea on sealing the end cuts. However I'm making these with vertical rather than horizontal slats, so I have a lot of end cuts on the ground. I'd need to be sure any sealer would not be toxic. (Hmmm... maybe I want to run a 2x4 across the bottom to keep those end cuts out of the dirt. Or use bricks or other material to support the planters(?).
I could use a liner but was thinking not because I wanted to give the plants as much room for roots as possible. I was also concerned that water trapped between the liner and the wood would cause issues. And lastly, it rains a lot here - we get about 40". If I put in a liner I'll have to cover them for 8 months or I'll have a bathtub.
Thanks much for the feedback.