"An 80m inverted vee, for example, should be up about 65' above ground at its apex and each end should be at least 10' above ground, else it will work quite poorly and have a lot of earth-induced end-effects."
I disagree!
I have used an 80-40 trap inverted V at two houses and several Field Days with the apex no more than 40 feet off the ground, and have had very good results for domestic QSOs. As in several hundred CW SS QSOs with a 100 watt homebrew rig.
Of course the higher the better, and it's important to get the ends up at least 10 feet. But an inverted V up at least 35 feet is a good simple antenna for your situation.
You *will* need to adjust it for lowest SWR if you use coax feed, but that's not hard to do.
"You could, of course, add a 20'-30' mast to the house and then use the top of that mast as the high point on an inverted vee."
That's what I did, except I only used about 15 feet of heavy-duty TV masting from Radio Shack. At the old house on RadioTelegraph Hill I used a vent-pipe mount,
and at my current QTH I use brackets meant for the side of the house. In both cases I used three brackets to spread out the stress.
Beyond about 15-20 feet, the mast would have to be guyed, which is impractical at my locations.
"If you do something like this, always install a pulley at the top of the mast, with a rope over the pulley, to raise and lower the antenna -- otherwise, any time you want to make an adjustment it will be a huge pain in the butt."
AGREED! But I gave up on pulleys long ago, and just use a large eyebolt. Eyebolts don't jam like pulleys and cost far less. Plus you can replace the halyard by splicing on a new one and pulling the whole works through. Be sure there are no sharp edges on the eyebolt to cut the line.
Another poster suggested 4x4s sunk in the ground to hold the ends, and I agree. An 8 foot 4x4 with several feet in the ground, and a 2x4 extension, will do the job for the ends.
At my current location, the peak of the roof is at about 26 feet from ground. About 14 feet of mast extends beyond the peak. On 80 and 40 CW I can work practically everything I can hear. It's definitely not the best antenna in the world but it's the best I can do for those bands at this QTH.
In my case I used homebrew traps for 40 meters because a full-size 80 inverted V wouldn't fit. You could use separate fullsize 80 and 40 inverted Vs with a common feedpoint, spread out maypole fashion.
As another posted said, the important thing is to get on the air.
73 de Jim, N2EY