I use basically the same thing, only mounted under the RV on the frame just forward of the wheels where it is close to the dump outlet.
Instead of the square fence, I use the 4" white leech field thin wall ABS pipe and position the holes on the bottom so that any residual water can drain out. There are also plastic floor grates (Lowes or Home Depot) that fit nicely into the pipe as a cap. By drilling a hole on each side I can slide a piece of coat hanger through the pipe&cap to hold the cap in place while traveling.
The other advantage to this type of holder is that you can make it the width of the RV, and thus accommodate a 20' Triple Wrap hose.
To mount to the frame, you can go through one of the drain holes on the bottom of the pipe and screw it (with a washer) into the frame.