I've been reading all the posts about verticals. If you have one fed at the base sitting on mother earth, you need about 90 radials to get good efficiency (according to the ARRL Antenna book). If you have a raised vertical and feed it above mother earth you only need something like four radials to get the same performance. (!)
For what it's worth, 90 radials is way, way more than you really need to get within a dB or so of perfect.
Just for an example, I have 27 radials that go out to the edges of a space that is at most 50 feet square. Many radials terminate prematurely because they run into my shed or the fence or something. They range from maybe 10 to 35 feet long.
I built a 10 foot tall 40m vertical and compared it to a full size quarter wave over this radial field http://www.n3ox.net/projects/n3oxflex
The shortened antenna with around 5 ohms (maybe a bit less) radiation resistance was only a little more than 1dB worse than the quarter wave. The shortened antenna had a base impedance of 6 ohms and the taller one a base impedance of 25 ohms.
If I look at the field strength readings and the impedance readings I can try to figure out my ground loss resistance. The results are pretty consistent with about 1.5 ohms of ground loss, with about 4.5 ohms radiation resistance for the small antenna and 23.5 ohms radiation resistance for the vertical (radiation resistance of verticals over real ground is complicated, hence the uncertainty)
But let's say I have about 1.5 ohms ground loss resistance. This explains both the base impedances AND the field strength difference between the two antennas. If my ground resistance is that low, the quarter wave vertical will be about 0.27dB away from PERFECT with a miscellaneous field of 27 radials from less than 1/8th wave up to 1/4 wave. This is a far cry from 90 1/4 wave or 1/2 wave or whatever but as far as ground return currents go, it's almost perfect for a quarter wave and so good that a 10 foot low impedance high base current vertical works almost as well as a 1/4 wave vertical.
I think people go crazy about radial recommendations for on-ground radials. It's important, and really sparse systems on the ground can be AWFUL. But it doesn't take many radials to stop having a really sparse awful system.
Do you think it would work well enough to go through the trouble? Or is getting the base up say, 12 or 16 feet not good enough? It just seemed easier and perhaps cheaper than laying out 90 radials.
I ran a 40m 1/4 wave with 4 straight-out elevated radials at about 15 feet at my first QTH. It was a fine antenna and I was very happy with it. It may be that you would rather drive the tractor UNDER rather than OVER your radials. I think 15 feet is way more than enough. N6LF has shown that if you're careful even a foot off the ground is a big help.
But keep a couple things in mind. You should use a good choke at the feedpoint for elevated radials. You can't use them as easily for multiband use. And on-ground radials are NOT the dire loss situation that many people make them out to be. You do not have to copper plate your field to get good efficiency.
I'm still digesting N6LF's latest article on elevated systems and need to look a little more but I think that if the elevated system is much effort
compared to an on-ground system, a modest on-ground system might be better for many reasons. 90 radials isn't just overkill, it's probably nonsense at least in terms of establishing a low impedance ground return. Big enough dense enough systems have some effect on pattern but that's not usually what people are talking about when they recommend huge radial systems.