I found that regular flourescent tubes (probably 20 watt each, maybe 40 watts) were not enough to bud very well. I ended up with small buds. I think it'll be a challenge for you to get good buds with just 2 tubes. You might try adding some CFLs, especially ones that are labeled warm, because that spectrum is best for budding.
This time I'm using a 150 watt full spectrum ECOPLUS CFL and my plant growth is outstanding, so I'm hoping that my buds will be bigger this time. Hope this helps!