You're right. The fares I saw were B class. The odd thing is that I don't get B class fares when just doing TPA/NRT RT, --it's only when I add BKK that I get the B class fare which is upgraded for every leg but NRT/BKK.

Thanks everyone.

The issue sounds do-able, but not advisable as there may be penalties I'm not willing to risk.

I'll continue to look at my options and hope that a B class comes up before the trip.