I am looking to add and on board air system to eventualy use for an ARB. bit where to mount it. Also place to mount a on board welder too?

Tim

Since you want air and a welder, what I'd do is relocate the battery to the rear with the welder, and put the air compressor and a small air tank up front.

What sorta OBA do you want? do you want a tank in the system so you can run tool's and air up tire's a bit faster?
Best place i have seen so far for a ARB compressor is in the factory jack storage compartment in the rear cargo area, i will have a air tank in my system and will mount it where my spare tire was under the truck.
The welder can be put under the hood in a seal'd marine battery box or in the vehicle itself.... maybe on the other side of the cargo area from the compressor?
just use your imagination :)

Just a thought, but is the 2nd gen lombar support air pump powerful enough to inflate tires? I never use that thing and I thought I could use it for something worth while. If anyone can help, that would be cool
-E

What about up above the spare tire? That is where my factory compressor is for the auto ride control and there is a truck load of room up there, especially if you have a body lift.

i have two compressors up above the spare for my air lift