I’ve always owned horses that got along great with each other, and I kept them together on trail rides.
I’ve used, at various times, both metal panels and electric fencing. Have used the metal panels free-standing, as well as attached to the trailer. The latter allows for a larger enclosure, but the trailer must be protected (and the horses protected from the trailer - watch out for fenders, for example).
One problem I had with the metal panels (tried two different types, both custom-welded) was that a very smart mare I owned figured out that she could push against the panels, stick her head through the rails if possible, fold them up around her body, and walk away where she pleased. It was amazing, amusing, and scary to observe.
This was a mare who, about every 12 to 18 months caused me to borrow a 120v charger from a friend (to substitute for the solar powered one I normally use at home) to light up our cross-fencing. She’d hit that once, get ticked, and then respect the electric fence for another year or so. Rinse, repeat.
When the terrain allowed, a portable electric fence, with step-in posts, a roll of tape, and a D battery-operated charger worked well, and gave my horses a relatively large area.
At some camp sites, my horses spent their free time on an existing permanent picket line, and appeared to do okay. But I only used my own set-up for one once or twice, for single night stays, so not a lot of experience with that.