I used a bushing that the truck guys use, its made of .188 thick steel DOM pipe with a massive composite center (WAY STRONG). There is a place here in CA that sells them, I think they were around 30.00 for 2. I first got the bags, they have a fully extended lenght and a collapsed lenght. Now with that you can figure your travel or for a better word your bag movement. Figure out how much room you have and find center of that, remember your bags have a fully collapsed lenght that cant change use that when making the mounting point ( you dont have to run the bag fully exstened you can use your cam ratio for that) Try to keep the bags at a 45 degrees or better, if you lay them horizonal they will start to sag in the middle. Mount the cam so it wont hit the bag or mounting support, you can get pretty creative here so what ever you think will look good will probably work. Now for your cam ratio. Figure how much travel you want your truck to move. Lets say 6 inches...Lets say your bag can only move 4 inches that means your cam has to have a ratio to make up the other 2 inches to get you 6 inches you wanted. To find that, take a diameter measurment times pie (3.14) and divide it by 4. You will get your ratio movement you need ( YOUr CAM SHOULD NOT HAVE MORE THAN A 1/4 CIRCLE TRAVEL) EXAMPLE--look at the clock 12 to 3----3 to 6---- 6 to 9--- you get the picture. Once you have got that make your rods and mounting brackects and there you go. Its not that hard, if you gave me your travel I could figure your ratio out for you or walk you through that part. If you post a pic of what your trying to do I would have a better idea of how to mount the center. I hope this helps.
Curt