The letters (dated from Feb 1943 onwards) are addressed in his own hand as follows:
384 Bty 117 Lt A.A. Regt R.A.
B.N.A.F.
I know that Regt is short for Regiment, R.A. is Royal Artillery and that BNAF is British North Africa Force. Other than that I have no idea what the rest means.
Some of his letters are written on headed notepaper endorsed "Royal Ulster Rifles", but other than that reference I can find no other mention of the RUR.
I have subscribed to http://www.forces-war-records.co.uk/ and can find only one reference to a soldier called Eric Johnson in the Royal Artillery, but his serial number is different, and I can't find any matching Eric in the RUR.
If anybody has any idea as to how my research should begin, I would be very grateful. I am ultimately hoping to find his medal card if one exists