I would only re-enamel for two reasons. One, you don't or cant remodel the bath area. Two, the tube has great value to you. Re enameling is expensive and it just isn't as strong a factory finish that can be baked on. Hope that helps.
Check the specs on the specific beams, they should have some ratings. To me 9.5in beam should be fine for 15ft depending on what it is holding. But again check the beams specs first.
