Chris, I used a 16 ga. stainless strip approx 2 1/4" wide and folded over each side 1/2"..this made quite a strong srap with a nice rounded edge that would not cut the rubber...the ends are folded again and drilled for a bolt and also an aluminum spacer to spread the load.
You really cant see the rubber under the strap, but it was a self stick foam that I got from Mc Master here in the states...probably available to you locally. The channel rubber is a great choice if you want to use that.
I also top mounted my tanks, but I believe in the straps to allow for flex and expansion/contraction as I think they are a better setup.
One thing I have done on some other setups but not my chassis was to weld a flat strip to the area where the strap pulls on the tank to avoid rub thru...I think it is more of an issue on a tank mounted for instance between frame rails such as a street rod.
The photo aint the best but you get the idea.
Good luck
Phil