CPR Aquafuge Hang on 18" Refugium on a 20Gal. Long?

[nano reefin]

Would it be okay to place an 18" CPR Aquafuge hang on Refugium on a 20gal. Long? Or would there be too much weight hanging on the back of the tank?
The dimensions are 19" L x 4.5" W x 12" H.
Thanks in advance!