Two awning companies make most of the awnings used on RV's today (Power that is)
Carefree of Colorado: All I can tell you about these is the name.
A&E, it appears they market these under different names, (IE: Dometic, a related firm) These I can tell you about.
The rear arm has a spring and slide system, if the awning starts getting heavy (RAIN) it shortens a bit and the water runs off.. or you can carefully pull it down but beware if you do this cause NIAGARA FALLS you want to be under the awning, NOT under the water flow.