Topband: TX antennas for 160m and 80m

[Rick Kiessig]

I'm interested in putting up TX antennas for 80m and 160m DX, and would be
interested in ideas/feedback on possibilities.

I'm thinking about an inverted-L, rigged in some way to support both bands.
I'd rather avoid Battle Creek Special style traps, if I can.

I'd like to use an existing 10m telescoping aluminum antenna as a start. I
can't go higher than that with the pole, but I can run a wire from the top
of it to a nearby tree that sits uphill from where the pole would be -
should allow for at least 20m of wire, hopefully a little more (so 30m+
total from antenna base to the end of the wire).

Establishing a good ground plane / radials will be a challenge. The property
is on a steep slope, part of the area is covered in dense foliage, and part
is my wife's garden. The good news is that soil quality seems pretty good
here, and I'm only about 300m away from the ocean, at about 100m above sea
level.

Questions:

-- Assuming I don't have room for a full quarter-wave on 160m, what should I
use for top-loading? Ideally something lightweight, easy to build and trim,
and capable of handling high power. Maybe just extend the wire back toward
the ground after peaking in the tree? The end might only be a few meters
from the ground that way, though.
-- What's the best way to add 80m? Would it work to run an insulated wire up
alongside the aluminum pole, using the same feedpoint? Or perhaps an 80m
1/4-wave stub, connected at the far end of the high wire, running right next
to it, coming back toward the base?
-- In order to support my solid-state amplifier, one of my goals is to have
an SWR less than about 2.5:1 at the antenna feedpoint. Am I likely to need a
matching network at the base?
-- How difficult would it be to support 40m on this antenna, as well? Can it
be done without traps? (my objection to traps is mostly from the complexity
and power handling side, not efficiency).
-- Given the issues I'm likely to have with establishing a good ground
plane, are there other types of antennas I should consider?

Thanks and 73, Rick ZL2HAM (ZM1G)