Here is something for you all to consider; Stauff hydraulic pipe clamps.

I have used the green plastic ones in a lot more applications than just securing hydraulic pipe runs. As a testament to their toughness: they are the specified choice for pipe runs in the very harsh North Sea marine environment on the folding arm type hydraulic cranes used on Oil and Gas field rigs and support vessels

http://www.stauff.com/index.php?id=1423

The trailer that I haul behind my car and pick-up has the tailgate hinged on three of the single clamps bolted to it's chassis, I use them as the stand pivot bearing on the cargo bikes I have made. I have used the double clamps to bolt the prototype single wheel trailer sub frame to the chainstays of a mountain bike and a hybrid.

These clamps cost pennies, and are extremely durable. They come with a threaded base plate for welding to frames etc, two part plastic clamp sections, a top plate and hi-tensile fixing bolts in BZP or stainless steel, and are avialable from size 6mm (1/4") though to 75m (3") diameters , and if you have an odd size to accomodate, the clamp holes can be opened up with a pistol drill and HSS bit.