my anecdotal review of towing while tuned was there were no issues while towing around 4700 on mainly flat roads while being on ZFG91 tune. im not sure about my E50 tune but id venture to say with it should be ok as long as staying out of high boost situations but again, anecdotal.
also in all my searching and lurking I have yet to hear
@ZFGracing speak up on if he doesnt recomend towing on his tunes.