Hi... sorry for the slow reply, it's been a busy last few days.
Anyway, you need to merge the objects, then fit all the UVs to the same map. You then need to cut the edges so it wraps.
I did just the fronts of your fence as a quickie so you can see... you'd need to add an additional set of cuts to keep the backpanel from wrapping. (Or cheat with an alpha map
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