I'm no structural engineer (hell i didn't even sleep at a holiday inn last night)...but that horizontal "reinforcement" in this picture (below) seems inadequate....some VERTICAL stocks even if it didn't cross the window would increase the rigidity.
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Don R.
'04 Haulmark (M42386) 42', 2 slide, 10kw -
Pictures
'04 F350 CrewCab Longbed 4x4, 50g aux tank & gear vendors dbl over