I'm a little confused on your "aluminum awning" idea....
If a towing trailer, perhaps it might be best to install a normal spring loaded awning. For example: http://www.argorv.com/suppliers/shad...ing_sample.jpg
When you travel, simply roll the awning in. Then, roll it back out when you reach your destination. And during mild or rainy wind season, lower its outer poles - to give it more slope.
If thinking of parking your trailer under a shelter (at a seasonal site or for off-season storage), perhaps a low cost soft material sheet shelter might work. For example: http://www.hisconw.com/images/rvpix/...-carport14.jpg
If wondering, I've created a removable "hard top" that goes over my TT's slide. This May, I plan to install it on my seasonal site' TT. This cover will also create a proper slope on our slide's roof. And, eliminate its water leaks as well. If wondering, I'll post digitila pictures this May. Perhaps a removeable "hard top" on your TT's slide might work as well?
Hope this helps in your research....