I would like advice about attaching reclaimed boards to a plywood base in order to form a counter top. Here is the situation:
I' making 8 foot section of counter using three reclaimed 9 inch wide shiplap boards. They are 3/4 inch thick and I plan to mount them on 5/8 inch plywood to provide a sturdy base and raise the counter to the appropriate height. The finish will be a pour on epoxy bar top.

The house is located in northern Iowa with hot humid summer and cold dry winters. I'm concerned about the boards shrinking in the winter and cracking the bar top finish.

The boards are quite rough so I don't think edge gluing them would work very well. My plan is to use liquid nails between the plywood and boards and putting screws through the plywood into the boards, but I'm pretty much flying blind on this project as I've never done anything like this and haven't been able to find good instructions.
If worst comes to worst I'll pour on a little more bar top in the cracks next winter.
Thank You!