WT: "I haven't had problems with any of the C. pepos growing vertical though I will say they grow better on an arch or arbor more than just a vertical trellis. The vines are huge and can seldom be contained by a vertical trellis alone. Then tend to go straight up and then look for something else to grab."
TSC:"Delicata would not be a good climber. They sometimes go up and over other veggies in my garden but have never voluntarily climbed up much. They have no tendrils so you would have to provide support. My Maximas, on the other hand, have easily climbed to the top of my 8' cedar hedge. The vine on the left keeps is having problems only because the hedge's branches can't support the weight of that squash. But the tendrils themselves are plenty strong."
R: "I've never tried to trellis butternut squash but that should work but so will you. Expect it to be a pain to keep all of it on the trellis, it can really spread out. I think you planted it pretty close together too, you may need to thin it when it starts to rum. You probably won't have enough room on that trellis to hold all of it. I tear strips out of old T-shirts to train things to a trellis. You may find you need to prune back the plant to keep it from spreading all over the vicinity. Be flexible"
CR:"It's a 16 foot trellis. I was thinking of growing 4-6 plants on it. Do you think that would be too many?"
R: "Should work though play it by ear. I grow tromboncini squash on a garden fence, it spreads as bad or worse than than butternut squash. Might be tight. and those panels are only 52" high, not a lot of surface area.
One advantage to using cow panels is that the holes are big enough that the squash will not cut itself in two when it grows in those holes."
How to Grow Squash on a Trellis v.1
You will need two vertical supports, such as stout wooden or metal posts, as your framework. Hammer the pieces in at an angle to each other in a tepee shape. The bottoms of the posts must go deeply enough into the soil to help support a heavy plant laden with large fruit. Space the posts 5 or 6 feet apart. You can also brace these posts with a cross angle at the base and across the middle to screw or nail into each piece. Growing squash on trellises requires a sturdy foundation as the fruit will weigh heavily on the posts. For larger squash, use a three post system for better stability.
As the squash grows, select three to five healthy vines to grow on and prune off peripheral growth. Build a framework of wire spaced at least 5 inches apart on the poles. Tie the vines as they get bigger along the wires to help support the plant. As fruit is borne, use fruit slings to cradle them and prevent the weight from pulling the developing squash off the vine. The cheapest slings are made from old pantyhose, which expand as the fruit grows. Growing squash on trellises is easy as long as you keep the vines tied and fruit supported as they grow.