Installation depth is 70 mm. Mounting position any, so vertical or horizontal busbars are fine.
Thermal derating — the number that matters at panel temperature
Rated 0.3 A at 35 °C. At 40 °C it's 0.29 A; at 45 °C, 0.28 A; at 50 °C, 0.27 A; at 55 °C, 0.26 A; at 60 °C, 0.25 A. If the panel ambient sits at 50 °C, the breaker is good for 0.27 A continuous — not the 0.3 A on the label. That derating curve is the spec that trips people up when the breaker holds at bench temperature but nuisance-trips in a hot cabinet.