I am trying to understand your question. Are you saying you want to plant 10 tomato plants in 8 feet(or less)? Do you intend to place the 42-48 inch end against the ground and arch over. I can visualize 4 plants in that configuration (2 on each end), or if the arches were together (long sides touching in the arch) then you might get 5 but that would be very crowded. So by crowding, you could plant a total of 10.

Turned lengthwise and planted ever 3 feet you could have 12 (6 per panel) or if you really crowded you might plant 7 per panel. I don't see anyway for you to grow 20 on two panels unless you are one who does a severe pruning of the vines.

There would be one row of arches, and the arches would span two planting rows. The 48 inch side of the panel would start on one row, arch over the aisle, and terminate on the other row. On each side of this arch, two plants would be planted to grow up the arch, for a total of four plants per arch.

Now, go over by one foot, and start a new arch. It would be the same as the first, etc.

So, the total length of this row of arches would be around 24 feet long (five 4-foot arches, with one foot of space after each = 24 feet). I bought 5 panels to complete this arch area.

With no plants on it, it would look very much like a non-skinned greenhouse... hmmm, there's a thought!!!

I've never been very good at geometry. Does anyone know how to determine what the height of the arch will be based upon how far apart the bottom edges are? I've been trying to google a formula or an answer, but am having no luck.

Just wanted to add that the row should look something like this when I'm done.

{{gwi:1330520}}

Sorry, I misunderstanding what you were asking and I thought you were trying to do that with 2 panels, not 5.

I'm not sure that picture worked... Here's a link, instead.

Here is a link that might be useful: {{gwi:1330520}}

You could to to stack them one above the other about 2 ft apart and have a nice grid for them to grow through. Imagine it like this:

That would make it 6ft high total, 16ft long and 4ft wide. The tomatoes would grow up through the holes in the cattle panel and be supported easily by them.

Here is what I ended up doing: More pictures are at my thread for new gardeners!

I don't want to be a party pooper, but so far, I haven't liked using the cattle panels in the garden. I made an arch once for pole beans, and they didn't seem to do that well.
I put one long cattle panel up with stakes and grew tomatoes beside it, but they didn't do as well as with my concrete reinforcing wire cages.
I tried to grow cucs up a cattle panel and they just wouldn't climb very easily, even after adding twine.
I have found that using that white nylon mesh netting is the best stuff yet for growing vining crops up a trellis.

This past year I had my first cattle panel arch in the vegetable garden. The arch is seven feet tall and five feet wide. I love it. Wish I had two more.

On one side I planted cucumbers and on the other side I planted Sun Sugar Tomatoes. I harvested huge amounts of both vegetables - of course we had lots of heat and rain this year. They grew together at the top of the arch. Very cool. I did use a short stool when I picked the veggies at the very top.

I did need to attach the very young vines with twist ties or string early on. Later, I occasionally had to pull and poke branches back into the mass of vegetation. As the tomatoes grew tall I would run thin string around, encircling that entire side of the arch. Every two weeks or so I tied higher every foot or so, because I knew that if I didn't, the next rain would knock the tomato branches down.

I plan to rotate sides next year, planting the same veggies. Or maybe only half cucumbers and half something else. Golly I couldn't even stand to look at a cucumber at the end of the season. I put them out by the street with a "FREE" sign. People always took them.