Watering and fertilizing wasn’t very troublesome, but I must tell you that the planter box was a stone structure, about 2.5 feet tall, well prepared with humusy soil and compost. I followed the Square Foot Gardening plan for homemade organic fertilizer, throwing on a few handfuls each week. When rainfall wasnt sufficient, I used public water, which I let stand in containers overnight, to allow the chlorine to evaporate off. I don’t remember clearly, but I probably underplanted the cukes with nasturtiums to keep the soil cool and mulched. I think the depth of the container helped support large root systems, which, combined with the angled "trellis", allowed the vines to get exceptionally long.
If it is impractical to build deep planter boxes, I’d be tempted to try the self-watering types. Or double-dig and prepare the soil well.
I have a couple pics of the old cuke arbor, but I couldn’t figure out how to add them to this post. While looking for the old pic, I found a pic of green beans and cherry tomato plants that also made it to the roof, but vertically. I had forgotten about them. Drop me an email, and I’ll email you the pics, if you like.