I bought 5 bristlenose plecs that way last year and they all survived the delivery. The box was clearly labelled that it had live fish and was to be handled with care
i reakon a couple of oxygen tablets in the bags will help alot.
also 1 fish per bag. oh and as there adults do triple bags, once old those spines are bloody sharp!! at work we had a monster of a sev come in and whilst bagging he got a bit annoyed thrashed aorund and hey presto a leak, with double bags!!
pad the box out with smaller fish bags filled with air as well.