have you actually tried your null termination method?
not that example , the lookup line might need to be lookup2 , the lookup line is not really relevant to the null termination array processing method

Code:
 OUTARRAY	VAR	BYTE(80)	'serial string output array
 BYTEIN		VAR	BYTE
 character		VAR	BYTE

	BYTEIN = 0
	WHILE OUTARRAY(BYTEIN)
		LOOKUP2 BYTEIN,[OUTARRAY],CHARACTER
 '		TX_BYTES2(TX_OUTPUT2) = CHARACTER
		BYTEIN = BYTEIN + 1
 '		GOSUB SNDCHAR2		'INCREMENT BUFFER POINTERS
	WEND