Trying to drive fluorescents from a forward converter without ballast is asking for trouble. You may manage with enough leakage reactance in the transformer to act as the ballast but it is pure chance.
The single ended things that work as flyback converters are safe, but they are not efficient and blacken the tube ends.
It is possible to make push pull self oscillating converters that are resonant, they are reasonably efficient but they murder the transistors if the tube fails to strike. I have had some running for 20 years but I wouldn't build any more that way.
I now use driven forward converters with resonant series ballast ( 3525 does this ok at 12v. IR lamp driver chips are better for 24v)
These work very well and with excellent efficiency but the resonant balast is critically dependent on the components and without specifying an exact inductor and winding scheme it would not be reproducible.
Unless you get these lamp drivers right the actual efficiency in lumens/watt can be so bad that you would be better off with halogen lamps. It is fairly easy to make something that will light but to do it properly with good lamp life and efficiency is a different matter.
Many of the low voltage drivers I have seen for marine and camping use leave more to be desired than I am prepared to tolerate.
Flux