I thought I'd tell people here how I setup my iPod Classic and my RSA Predator together in details. I'll add pics tomorrow as the light here is bad and at work it's much easier to take good pics

I don't use a casing anymore on the iPod, and the metallic back of it was sliding a lot against the metallic casing of the Predator. So what I did to remedy this is to use the leftover rubber part from a pack of 3 big rubber feet I had laying around and sticked it on top of the Predator (this would have worked also by sticking it on the back of the iPod). That way, when pressed together, the iPod and Amp don't slide anymore.
Next, I used a few velcro straps (the kind you can use to strap together a bunch of cables), cut it to size so they wouldn't be too large and strapped them around the setup, at 2 different places (underneath the screen and underneath the click wheel) very tightly.
I left the sticky part of the velcro strips on the outside so when I put the setup in a bag, the whole thing stays in place.
Looks quite good and is very stable. Pics tomorrow

Edit : Here are the promised pictures :
First, I applied the leftover from some rubber feet I had laying at home (why I kept those in the first place, don't know, but they came in handy!). This is to prevent the iPod's metal case to slide against the Predator's case. They kind of "stick" together after that :

After that, I used those velcro straps and cut them to size :

In the end, this is what the setup looks like from underneath and above :


Everything is pretty solid. If you don't want to have the velcro stick to anything, you can put rubber bands or elastic bands on those of the velcro strips. I'm also tempted to try black tie wraps with a short elastic band underneat to protect the player and amp...