Ed,
I'm certainly no expert on wind loading, so don't take any of this
as 'gospel'. Having said that, I've found that winds in the 75 mph
range can tear up almost anything, even if it is guyed. That's from
living in "Tornado-Alley" and seeing things laying on the ground that
shouldn't be. I figure guying is at least a sort of good insurance
thingy.
If you get a lot of salt water where you live, I'd also take a few
precautions about treating the antenna in some way to help prevent
that corrosion. No ideas about that since I don't have much salt
water where I live. There has to be something that will help at any
rate.
And lastly, your vertical at 20-30 feet tall just ain't gonna work
super-well on the lower bands where it's not going to be sort of close
to 1/4 wave length (mobile 80 meter antennas come to mind). If you
are happy with that performance, then big deal, who cares, it works.
- 'Doc

(None of these thoughts are all that 'fantastic', mostly just 'what-
if's and 'common sense'. Also probably included in that list of
mistakes I've made before.)