Tiger Mate,
Given that you referred to a specific airfield, I think the answer you seek can only come from a search as to what was actually on site at the date you specify, if it's to be authentic.
The station Form 540 will reveal the deployed RAF Regt/AA units present. From this you can find the weapons issued to those units and hence depict them.
Your painting -which is looking good - suggests that one is looking along the line of a 'paved' strip or hardstanding. I think it unlikely that any obstructions (weapons pits) would be in the foreground, perhaps off to the side therefore.
Old Duffer