What about mounting the mirrors above the solar panels, facing down?
In such a way/angle that:
- when the sun is low in the winter, it hits the underside and reflects to the panels,
- when the sun is higher in the summer, the mirror partially shades the panels, helping reduce the risk of overheating.

They could also be mounted vertically on the sides, focusing the sun from due south in the winter, but shading due east and due west on summer mornings/evenings.

That sounds a good approach, if the mirrors could be mounted safely and firmly so they were not converted into a kite in the first high wind. Not impossible by any means, it would just need a bit of care.

For 1 reflecting more light on solar panels voids their warranty. 2 unless you can reflect the light over every single cell you won't see any increase in output on traditional panels.

After looking into it my idea is to enclose my pv array in a fenced in area with it’s inside walls painted white to “brighten” up the area.

A Mirrors reflection will cause a hotspot on the panel that over time could likely damage it.
Using a softer reflective material like the white Tyvek ( very reflective ) or say flat white painted plywood would be safer (cooler) and likely still boost the lumens.

I’ll test this theory using a diy Tyvek reflector this summer then test again in winter to compare in different temperatures. A 20% gain in the winter would be a big win