So today I was out in the back part of the property working on the new ramp to my shed. I don't have electricity out there yet so I'm using my 2000 watt inverter to run my sander. I was using my little 18 volt compressor to use as air source(it kinda sucks) and got to wondering, do you think I'd run into issues if I used the 12 volt lugs on the back of the inverter to hook my 12 volt Smittybilt 5.6cfm compressor to? I wouldn't run the inverter and the compressor at the same time but I was thinking of the possibility of a box that would hold both and just require one plug in.

Hard to say. The terminals on the SB air compressor are large. It pulls a bit when on and the rig should be running while doing so due to the load. I think clipping the alligator clamps off and using a new plug, and just switching plugs when you need would be best. However if you plan to run any tools off that compressor you are going to need a tank..