I travel a lot and use a MacBook Air as my primary machine with an iPad Air for secondary tasks. Occasionally I find it would be useful to have a second screen, but because I don't have a fixed work location carrying around a second monitor would be troublesome.
I've seen apps like DisplayPad and AirDisplay, which seem really useful. Unfortunately, all of the ones I've seen require you to be on the same Wifi network. This is a problem for me; quite often I use my iPhone's 4G network or have no network at all.
So, basically I'm looking for an app that will extend my desktop onto my iPad as a second screen over either Bluetooth (though I feel this may be too slow) or over my USB/Lightning cable. I've seen TwomonUSB, but currently that is Windows only.
Are there any other solutions out there?