jtnc- I don't have any play in the boards. They are pretty snug to the frame and do not really slide in any direction. We walk on them, strap gear to them, etc. and they don't move.
When I was making the boards, I did a bit of experimenting on a scrap piece of wood. I cut a few different size holes until i figured out which size was ideal/most practical (1 1/4"). Once I figured that out, I cut some holes at different distances from the edge of the board, until I figured out which provide the most security/stability/least movement when strapped to the frame (2 3/16" I believe or maybe it was 2 1/4", shouldn't matter...).
Also, I have straps connected to the frame parallel to the running boards as well as perpendicular. This probably helps the most with keeping the boards in position.
I've never had any trouble with the buckles getting stepped on and loosened.
I used a hole saw so I could run more straps through the holes in any direction. This has come in very handy for strapping gear or strapping DIY thwart coozie holders
to the boards (I cut another slot in the bottom of the holder to run the strap across the bottom).
Dude- Behr Deckover. I like it because it provides traction and is relatively resilient. You can get it in custom colors. I have to do minor touch-ups once a year on a few wear points. But that's it. You can control how much texture you get out of it by varying the nap on your roller and using different rolling techniques.