Sunbrella flimsy? Hardly... sunbrella is used extensively in Sailmaking, awnings, etc. it is solution dyed, so it has wonderful lightfastness.  Think of a carrot versus a radish. Sunbrella is dyed all the way through like a carrot, whereas most fabrics are like radishes, colored on the outside only.  A 12 ounce Sunbrella can take very rigorous abuse.  Just think of a sail, the constant exposure to sun, wind, sea air, etc. Tough stuff.

I don't think it's appropriate for indoor use, although the company make some indoor fabric.  I'm pretty sure that Sew-fine uses nylon fabrics and nylon threads. Pretty durable stuff. Glass tend to filter a lot of UV too. A good coat of scotch gurard, and nylon should last for many years.

Troy