I just built such a trellis out of bamboo this weekend. I have 8 indeterminate toms in two rows across a 4 foot-wide bed. The trellis is on the north end of the bed with X-shaped supports on the ends, 2 bamboo supports running between the tops of the two X supports, and string running down to each plant. The plants are currently pretty bushy and maybe 2.5-3 feet tall. We'll see if it works.

steve - I did it last year, and it worked fine.

EG

Question.... I also did a double sided trellis, but am thinking I may have planted too closely. Here is what I did...

I dug a 1 foot trench, 1 foot deep, and with proper dirt and manure and such. I built the trench, going east-west, going through the middle. I have one row on the north edge of trench, and the tomato plants are spaced 15 inches apart. Then, on the south edge of the trench, I have another row, also with the plants spaced 15 inches apart. Thus, they are staggered I guess. Here is example below...
.'''15in
X---------X---------X---------X---------X
===================trellis======================
-----X---------X---------X---------X---------X
7.5in
So no tomato is closer than 15 inches to another at the planting hole, but then when they grow on the trellis, they'll be only 7.5 inches apart (15 inches divided by 2)

Did I screw this up ? Are they gonna be too crowded on the trellis ???? Thank you in advance.