Hello, Arno and Dave,
I agree with you Dave, a vertical by the sea,with the conductivity of sea water, is nearly 10 db gain.
By the sea I use a full size vertical with one radial made of Buddipole parts. It is a monoband affair, but I can change bands easily by ajusting the whip accordingly, and I fine tune with the antenna analyser.
But for your wire antenna, if you can have a small telescopic fiberglass pole, which can be easily hook up to a picnic table or something else with bungee cord, and at least one radial.
An alternative you can use a EFHW like the trail friendly by PAR END FEDZ which cover very well 40/20/10 meters. This one too can be hook-up to a fiberglass pole, and used in an inverted-L configuration, if your pole is too short.
For this antenna, you ca read reviews which are very good: REVIEWS 263 and the average rating is 4.9/5 not bad.
http://www.eham.net/reviews/detail/3632Now the web site with all the informations you will need:
http://www.lnrprecision.com/Personnaly I have the trail friendly for 40/20/10 meters, rated at 25 watts max, and I adjusted the antenna each time I'm into different environments.
I can cover the whole 20 meters band with an SWR between 1.1 up to 1.3 to 1
Rougly 130 KHz on 40 meters, that is enough for me as I stay into the CW portion of the band, between 7.0 up to 7,125. and believe or not, one full mégahertz = 1000 KHz on ten meters below 1.3 to 1 from 28.0 up 29.0 MHz.
For FM/AM portion of the band I use the internal tuner of the KX3.
I plan to built one next spring for other bands.
So I hope it helps,
Let us know of your progress, and in the mean time, we wish you all the very best in 2014.
Season's greeting,
72 Michel VE2TH