I was wondering if anyone has found a different location to install an Airlift compressor besides the trunk? I was considering doing an axle back and installing it where the muffler currently is.

 

Sure

 

i mounted a single compressor in the trunk where the foam USED TO be.. passenger side.. used a spring loaded isolation kit.. works great.
You can mount most any compressor outside but need to pay attn to air intake and you will get much more physical wear and tear on the item.
Id still run the air intake thru the supplied tubing into the inside of the car, clean air.
Also dont overheat it.