I think because space, money, and aesthetics are limiting factors, I
need to use precision to my advantage rather than size or height, and a
4 square may help there.

Sounds like too much work for my lazy a$$... :/ If you did that for
20m, it's kinda stuck , as far as spacing, etc, for good performance
on the other bands. Me, on 20m...I'd be using my mobile antenna.
And I'd probably be hanging pretty close with any "fancy" antenna.
When I'm mobile, 20m up, there is *no* disadvantage vs being at
the house on dipoles, etc.. At least as far as talking. On 20m, my
mobile is LOUD. I can work dx at the drop of a hat, and still do
well stateside. Even on 40m, there is little real disadvantage to
being mobile vs the dipole at home. Even in the daytime. Say if
I'm 20-30 over 9 at home, and drop to 10-15 over 9 in the mobile.
Doesn't
amount to a hill of beans... Same for 75m. But in the summer on 75m,
I do recommend a dipole/loop, as it will be worth quite a bit in
getting
over the noise running NVIS. I could talk with the mobile just fine,
but the dipole will make me "full quieting" to use an expression...
It's like throwing on an extra 500w when you are shooting upwards...
I wouldn't underestimate how well a *good* mobile antenna could
work on the higher bands. If it's mounted up high on a trailer, etc,
it should work well. It's like being on a huge car. The only problem
is
changing bands...You need to be able to reach it to change taps,
etc.. But that can be easy with a quick disconnect. That's what I
use on mine. I can't reach my coil when the antenna is on the trucks.
With the disconnect, a twist, and it's off. Also good for theft
prevention..
A good screwdriver could be an option too.
Not saying you can't try other antennas, but just saying , a good
mobile
will get the job done, all by itself. And it's pretty simple and easy
to
look at visually. It will often outplay ground mounted trap verticals
with mediocre radial systems on the higher bands.
MK