This enclosure has two recommended ways of mounting on a vertical mast: either vertically or horizontally. These options are highly suboptimal in most applications. You can collect more energy by mounting the box at an orientation that is determined by geophysical location.
One possible exception is when the box is deployed in a location with heavy shade, like in a tree. A vertical mounting might actually be best in this case. But out in full sun, mounting at an acute angle is likely to be much better.
Where I live, the optimal tilt is 37 degrees (I live at 39 N, which closely approximates the ideal tilt), and the optimal azimuth is 173 degrees. I could lose 30% of potential solar energy by mounting the box vertically instead. This loss is greater the further you move south. Mounting horizontally can be worse, since dirt and snow are more likely to accumulate on a horizontal surface. The 37 degree tilt can allow snow to slough off of the solar panel, and can help rain to rinse off dirt. Here is what the insolation looks like for me versus orientation:
You can find your ideal PV attitude in the US here: Annualinsolation us - Solmetric. If you are in the Northern Hemisphere, but not in the US, you might be able to find a city in the US that approximates your lattitude. If you are in the Southern Hemisphere, you might be able to use a similar (but complementary) trick.
One way of providing a proper mounting is to use a bracket that is bent to the proper angle. However, there are commercial alternatives that are designed to provide arbitrary mounting orientations, while allowing easy access to wiring ports on the box. For example:
https://www.aliexpress.us/item/3256806157714601.html
Mounting the box on this aluminum bracket has an additional potential benefit of providing cooling. The mounting bracket should help draw heat away from the bottom of the box. The bracket would be shaded by the box, which would enhance the cooling potential of the bracket. I applied aluminum tape on the inside bottom and on the outside bottom of the box to act as a heatpipe and heat spreader. This can help extend the life of the battery.
One downside to the bracket is that it can potentially impede RF propagation. You will want to orient your BLE and LoRa antennas to avoid such interference. For my mast-mounted application, I use a Yagi directional LoRa antenna pointed North, and the bracket is pointed South. I use a PVC (nonmetallic) mast, which is important for maintaining the Yagi beam pattern, along with staggering the antenna and the bracket vertically.