DC power connections
I'll leave others to comment on suitable connectors BUT

DO NOT unplug highish-voltage DC connectors with the system live.
DC can draw a really really really really nasty arc - how nasty you may never get to believe if you try it. I can arc weld (with a rather modest arc) from a 250  Watt, 30Vmp solar panel! At 300V with 500 mA+ available the arc may be more impressive than you'd hope.

A friend of a friend disconnected an N00V solar panel connector under bright sun conditions. He survived but ended up in hospital. (He had some kW available but your 150 Watts+ is not unimpressive. 

I'd also be very wary of running the 12V and 300V together in a DC highish-V system. It should work just fine [tm] but on the day it doesn't the fan circuit may trivially easily become part of the 300V circuit by way initially of arc and soon thereafter via carbon tracking.
Ask me how I know :-).
I've experienced occasional incidents over decades, but relatively recently, a 3 kV isolated Hall current sensor had an in-IC 50A shunt. A battery short circuit of a 40 Ah LiFePO4 battery caused the Hall shunt to go O/C, and arc formed, the plastic IC housing carbonised and the 24V current entered the LV system. The 3 kV initial isolation counted for nothing. 
Your 300V would be unhealthy for 12V fans, low voltage wiring and people in immediate contact.