I replaced a plywood floor that someone had put in previously with normal pressure treated timber. This just a utilitarian repair, not a show truck. It has stood up well since I did it. I like the fact that water can drain through it and not get caught at the sides or ends.
Here's the video:
https://youtu.be/gCGLkEqbrjE
Here's an extra video giving crossmember dimensions for the 41 bed.
https://youtu.be/lthqLNFKLfY
Hopefully you might find the info useful. Basically you have to space up the wood floor so the new bed floor sits level. You could locally thin out the planks where they sit on the raised parts, (I didn't) to get the floor as low as possible.
Mine works well for me. You might want something fancier, I don't know.