I attempted to make my own Venturi type system for my previous rig, a Class C. First time I did it I used a piece of PVC pipe and it got to hot and folded over. I then with a different type but allowed for more distance between the steel pipe and the tube and attached it differently. Worked but I paid myself ~$5/hr fooling with it.
One of the best options I saw was using a piece of aluminium gutter down spout, light weight, has structure because of the rigs and you can cut it in two for easy storage.
When we bought our current rig we just bought the venturi.
2002 Monaco Windsor 38 PKD
2005 Jeep Grand Cherokee w/5.7 Hemi