I fitted a 4x8 sheet of 1" thick plywood to back section of my S-10s box. Then bolted it down through the holes designed to hole the topper on.
Three is plenty of room for two shooters shooting across the platform and is plenty stiff enough for even shooting my 36 lb 50 BMG.
Nice thing is that it is very portable!!! Just about the right height for me being 6'3". It is a bit short for taller shooters but even better for shorter guys and ladies.
Take it off in the winter to save it from the weather.
Nice thing is when it finally gets to the point that its time to replace it I will simply go get another sheet and fit it the same way. $35 and your good to go for many years.
Only real negative is that when its really windy, the truck does rock in the wind a bit. Still if its really windy, I generally do not shoot extreme range.
This works great for full size trucks as well but you may need to screw on some supports on the bottom of the sheet of plywood to stiffen it up. This is easy, take the proper length of 2x4 and use good wood screws and secure the 2x4s to the bottom of the platform in an X pattern, This will stiffen the platform up plenty for any rifle up to 30-35 lbs with all the accessary gear.
Remember to leave the support 2x4s short enough to allow clearance for the plywood to overlap the bed rails.
If you have a new truck I would not recommend this as there will be some wear on the bed sides from shooters rubbing on them and the board can cause paint ware on the bed rails.
Good Shooting!!
Kirby Allen(50)