Halogen bulbs and RHP

[Homebody]

How many halogen lamps would I need for a 6’x30”x2’?

I would see how the RHP does before I added additional heat. That a big enclosure, but that also a big RHP, so you may not need additional heating. If you do need additional heating, I don't know that I would go with halogens. That's a lot of light for nocturnal animals. I'd consider a CHE or UTH.