OSB wouldn't last long outdoors, especially if you start poking holes in it and it starts to get wet.
Another suggestion related to building target stands:
Nothing worse than building a target stand only to see archers destroying it by hacking & digging arrows out with all sorts of knives, chisels, screw-drivers, etc.
Where the wooden H-frame is most likely to be struck by arrows, consider mounting some "sacrificial wood" on the exposed surfaces.
Any cheap wood attached to the main structural pieces using (e.g.) 9mm wooden dowel rather than metal screws.
Errant arrow now embed themselves in the sacrificial wood: so archer can now hack at this instead of the main structure. Or maybe archer can remove arrow and wood, place wood on ground, put foot on wood and pull arrow out.
Ok, some arrows might go all the way through and still hit the main H-frame, but now do far less damage.
Just a thought.
V