Try a large magnetic loop for the low frequencies. Its a loop with a capacitor on one point and a way to feed it. You can set them on the ground. Just keep it away from metal objects and living organisms

. And don't touch it when its transmitting or the high voltage could damage you.
Here's a cool website about a guy who has a fairly big magnetic loop ( Read the paragraph "160m Performance Recap"):
http://www.brisdance.com/vk4amz/Loop5.htmlHe said it works better than other antennas for close and far contacts. And even though its not super efficient at the low frequencies, it looks like its a lot more efficient antenna than what most other people have for low stuff.
Here's a handy calculator:
http://www.66pacific.com/calculators/small_tx_loop_calc.aspxAnd another loop website to help out with feeding it:
http://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm#construction-Mk-2-Copper pipe is pretty strong stuff. Its easy to solder. Ask a buddy, he might have all the tools you need to solder. I bet you could prop it up with one 2" PVC pole and some tethers.
-The narrow bandwidth is the biggest pain in the butt. To adjust it you need to reach up and twist the capacitor manually or make a motorized remote adjuster (probably not going to happen).
But if you only need it for a single frequency:
-get a cheap variable capacitor
-tune it to your frequency
-measure the capacitance on that capacitor
-make a capacitor with the capacitance you need by using a length of coax cable (coax that can resist high voltage).
-And theoretically this coax capacitor could be adjustable a little bit by some stripping off of the protective outer layer so you have the woven shield exposed and you could slide the shield up or down as you need and keep it in place with a zip tie or string...
This youtube video has a magnetic loop. Notice its pretty * portable *.
https://www.youtube.com/watch?v=s3oP6VAG3gs