It would depend on how your church designated and recorded your pastor's compensation package.
Did they record the pastor's salary as 30,000 and then designate an additional 18,000 for their housing allowance? Or did they designate the $30,000 to be divided as you mentioned?
This information should be written somewhere...in the minutes maybe?
If he received $48,000 then $30,000 (regular salary) will be recorded in box 1 and $18,000 (housing allowance) will be recorded in box 14. IF he received $30,000 then $12, 000 (regular salary) will be recorded in box 1 and $18,000 (housing allowance) will be recorded in box 14.