I tried making my own as a drop-on attachement to my existing sluice. It worked OK, but I struggled to get enough water flow in the creek I was in. I ended up building a rock dam AND gaffa taping a garbage bag to the lower level and extended it out across the dam wall. That ened up being good enough at the time, but it hasn't rained there since so I haven't tried again. I have since modifed the lower level to have a big rubber sock that funnels water into the fluid bed, but I haven't tried it yet due to lack of water.
I think I will end up getting a Croc Gold Trap eventually, for the following reasons:
1. They are considerably lighter than my wood + aluminium construction
2. The agressive funnel shape naturally increases water flow where its needed (at the grizzly's and at the tube openings into the fluid bed).
In the meantime, its fun to create my own and experiment.
Regards,
TheWolf