Need help with mounting a backrest on the snowmobile

I picked up a decent back rest with a rack for my snow mobile. It fits decently around the seat in the back and it partially rests on the existing aluminum rack on the back of the tunnel.

I'm not sure how to best attach it to the snow machine. First of all it's steel and the snow mobile has aluminum so welding it all together is not an option. I'll need to fashion some kind of a steel bracket to bolt it onto the snow machine.

Here are some pictures of what it looks like loosely sitting on the back of the machine:

 

Not everybody at once now....

Ok - I was thinking something like this, for Step 1. Fabricate a steel bracket that would be welded up on top and bolted on the bottom. It would fit around the aluminum tube without touching it. Thus, all the pressure would be transferred to the two bolts that hold it fast to the tunnel. That's step 1. Comments?

 

Exactly what I was thinking. Then maybe some rubber bumpers or split heater hose between the two tubes on each side?

 

Maybe use the bumpers or hose to stop the rattling and support the back.

 

This is what I ended up with. I've purchased the brackets at Home Depot, some parts for the fence. I've trimmed and bent them to shape and this is what I ended up with. The connection is strong and the rack feels solid even without any connections to the tunnel itself. I think I'll leave it like that and try it out before I mess with.