I have a number of rounded feeder pens from 34" hog panels. Use from 8-12 per pen. I overlap them and use wire rope clips (look like little u-bolts) to bolt together on the overlap. The pen will stand up by itself and is really solid. If you can get the t-posts in the ground good, anything more than one wired in the middle of each panel would be overkill. Would be a big waste of time and effort for me to use one in mid and both ends on each panel. In my rocky country I sometimes have to use a big hammer drill to set posts. Basically they keeps hogs from shoving the pen around but do not serve to hold up the panels since they are self supporting. My pens have been up for about 5 years in heavy hog country and we have everything from WT to aoudad, to axis in them regularly. Still as good as the day I put them up.

I just built a twelve panel square pen using 12 t-posts and 12 rebar posts in the middle. The rebar posts are easy to drive and provide plenty of stability.