I've been though this recently. My original "fixed, linear array" was very similar to your first drawing - a single axle, cross-arms and vertical supports. It works but the degree of flex along the panels did (and still does) concern me.
I recently made 2 (really 4) extra arrays, and re-thought it. Like you, I considered a triangular-section frame but it had too many down-sides with making the array tiltable. In the end, I made it out of structural 2" gal and fittings, some pics to follow:
I used readily available pipe "T" fittings to top my posts, and a length of pipe as a runner. I bored the middle round in the lathe, and will add either brass or HDMW or similar sheet inside as a "wear" surface.
The posts are set solidly into the ground. The tyres filled with concrete are to stop grass and weeds growing around the posts, and make it easier to buzz round it with the line trimmer. Here is setting out the posts all in the same line, and same height.
Checking they're all true and in line
What isn't obvious here is that this is actually two arrays end-to-end. The two halves can move independently.
The cross-members are Z-section, rolled, punched and cut at the positions I nominated, and surprisingly cheap. The pipe spacer is necessary for alignment, the reason will become obvious shortly. Long U-bolts are easy, strong, affordable and don't require welding.
With the cross-arms roughly in place, the long arms go on. (Also 100mm Z-section, rolled and punched and delivered ready to lift and bolt in place). The spacer gets the upper face of the Z section and the pipe "axle" at the same height.
While I don't really need to change the angles, I wasn't going to be happy unless I could. One actuator per array lets each array swing 50 degrees either side of horizontal, which is plenty for my site. By making the arrays completely symmetrical, the weight is evenly distributed either side of the axle, and minimal effort is required by the actuator to position them.
Putting the array horizontal (or near enough) made putting the panels on a simple, one-person task.
Cables were run in conduit which was then encased in pipe for mechanical protection, so I didn't have to dig very deep (this is my roof after all!)
Totally happy with the way they turned out, work great, did everything myself, unaided. I did end up doing a tiny bit of welding on-site - the reinforcing mesh for the concrete in the tyres, I welded to the posts. Overkill, perhaps, but they're not moving