Even though I had thought about using cedar but it was starting to make this to complicated. This is my first rail and style door and I am making it out of treated lumber for exterior access to crawl/basement space. I have milled down 2x8's into 4" styles, a 7" bottom rail, 5" lock rail & top rail. In the middle I am planning on using a 3" piece or narrower off cuts to connect the rails (not sure if that is a middle style?).

Question: How to assemble the panels? I have cut a 1/2" groove in the rails and styles that matches my 10mm mortice chisel that I will use to cut the mortices. It is a little over 3/8" where the panel material will go. My idea for the panels are:

1) Tongue and groove the 3/8" thick slates that make up the panel but not glue them together to allow for expansion and entire panel will also float.

2) Make a panel by gluing up treated pieces and plane a bevel to fit in the 3/8" groove.

I have Tite Bond III for glue but I have never worked with a treated panel or use glue on an exterior piece. Do you think a glued panel can hold up? House has a wide overhang but some splashing will hit the door at times. Thanks in advance for any help or ideas. This is my first door build.