Barn door panel insert

[Jude Lancaster]

Hi there. New to the forum, semi-skilled woodworker. I am making a barn door for my house using 1 1/2" red oak for the frame and 7/16" oak to make the panel insert that will go in the frame.
My question is, what should I use to keep the panel in place and allow for expansion? I can't find space balls that are large enough as they seem to be mostly for cabinet doors and are .26" diameter.
Any advice would be greatly appreciated.

[Jamie Buxton]

You don’t need space balls. At the middle of the rails, drive a nail through rail and the panel. Of course, center the panel first.
Doors were built like this for many years, long before spaceballs existed.

[Kent A Bathurst]

What size is the panel? What’s your ideal diameter for the space balls?

[James Pallas]

Pieces of rubber tubing or backer rod for caulking. Many sizes to pic from.
Jim

[Mike Stelts]

There's an advantage to backer rod: Wind won't blow through the crack, like it does in my circa 1850 doors.