Steve, G0KYA blogs about HF propagation and antennas. Recently, he posted plans for a 10m “Slim Jim” antenna made from 450-ohm ladder line. At more than 9m tall, this antenna isn’t very stealthy, but if you have a tall tree to hang it from, it should be a great performer.
While you’re on Steve’s site, make sure you check out his two books, Stealth Antennas, and Understanding LF and HF Propagation. The latter is a compilation of articles he wrote with Alan Melia G3NYK for the Radio Society of Great Britain’s (RSGB) RadCom magazine. You can’t beat the price. It’s a free download!