I have sandy soil. It's not like beach sand, but no clay whatsoever in it. I have amended it over time, but I have to constantly water the plants. I have several rainbarrels collecting off the house and the garage, but there are times when there is no rain for periods.

I don't quite see what your method is. Even though you may be planting in the trench, when you apply water, it will still leach into the ground whether it's in a trench or on surface.

I water by filling the basins and trenches. The seeds, and the roots of the plants, are at the bottom where the water concentrates.

When I had them on hills and ridges, the traditional planting method in clay soil, I could water all day and the water would all run off the surface to puddle in the nearest low spot and soak in there -- straight down without spreading sideways or working back up via capillary action. The surface of the hill/ridge might look damp after running a sprinkler, but it was only a film one sand-grain thick that would break like a soap bubble when touched and reveal dust-dry soil.

Putting the seeds in the basins and trenches in the sandy soil gets the seeds/roots and the water into the same place. :-)

oh I get that clever!, I hope it works, you must let us know.
I saw this post early and thought the same thing as naturelle, but as they had asked the question I wanted to I didn't add

Very nice, and great trellis! I have the opposite problem ~ solid clay LOL

i have clay but i use the same techniques. Makes it easier to water the crop and keeps the water off any potential weed seeds.

Nice illustration.

Nice picture! I have been wondering how others here handle watering since different conditions call for such varied solutions. With my fast draining soil I do the same thing as you do, it also really seems to help my germination rate with any of the larger direct sown seeds. I generally widen the trough as the plant grows to broaden the area the water sinks into to.