Lowband planning: 160 and 80 meter antennas

Background
Tower/Site Considerations and Operating Goals
Remaining questions
Lowband antenna choices

Background

In the fall of 2007, I was able to install my first amateur radio tower. While this certainly was a huge improvement over my humble Butternut multiband vertical, my new tower had a major shortcoming... a lac N0HR ham radio tower k of antennas for the low bands: 160 meters and 80 meters.

A few years ago, I acquired a multiband commercial antenna called a half-sloper. This antenna, the Alpha Delta DX-B, is a trapped, quarter wave single wire sloper for 160, 80, 40 and 30 meters and has been installed at the 55' level and slopes to about 25' off the ground. I bought this at an estate sale for $15. I did not have high expectations - but wanted to try to get a lowband antenna installed prior to the winter 2007/2008 season. The Alpha Delta DX-B performance was disappointing - especially on 80 meters. It is definitely time for a new approach to 80 and 160 meters.

Tower/Site Considerations and Operating Goals

With every amateur radio antenna installation, many factors must be considered: safety, surrounding objects, costs, etc. Like many hams, I am somewhat limited in terms of space for lowband antennas.

Here are a few factors that I need to consider:

A 70 ft. self supporting ANwireless tower topped with a 4 element SteppIR and a Cushcraft XM-240 2 element yagi.
A distinct lack of high/natural support structures (no trees!). Our small neighborhood was a corn field 10 years ago and we simply do not have many large/solid trees quite yet.
No radials at the moment - but will plan to install several (at least 16, ground mounted).
Only running 100 Watts (for now) - will likely add an amp.
A medium-sized lot (0.6 acre) in a somewhat rural setting, surrounded in the back by a chain link fence.
DXing and contesting would be my primary needs for this antenna. Favoring, but not limited to CW.
XYL would prefer very few wires running across the yard. The sloper was OK.

Remaining questions

How can the matching network be built such that the antenna can be remotely tuned across both 160 meters and 80 meters?
Will mounting the antenna near (<3 ft.) the self supporting tower significantly impact the design?
Are there improvements in the design to be made?
Where can I find components for the matching network and trap?

Lowband antenna choices