Which Plywood for a Load Space Tiedown floor?

[nwoods]

I have a Land Rover LR3, and I am thinking of installing a plywood floor into the rear cargo space and mounting tie down points to it. I do not have the 3rd row of seats, so I am not too worried about removing the flooring very often.

I have purchased the Slide N Lock system from Sierra Expeditions (nice vendor!)

My question is: What thickness and grade of plywood should I use?
Can I get away with 1/2" (15/32's) instead of 3/4"?? What works for you guys?

TIA

PS: I should add that I intend to secure this new flooring to the existing hold down points already in the LR3. There are 4, one in each corner. I thought maybe I'd use a trick learned from TravelToad (on other forums), buy using a gate latch:

 

[LandCruiserPhil]

Plywood comes in different grade the more plys the better/stronger the construction. With that said 1/2 ply will work but more important would be the use of large fender washer when you bolt you Slide N Lock system to the plywood.

 

[MaddBaggins]

I used some stuff thats 3/4" 7 ply marine grade. It was a bit pricey and has held up to a lot of abuse the last 2-3 years. And like Phil said, use big fender washers to spread the stress out.