Most missions are done with the Fortuna.
With the grey codex, you got the 'conversion launcher' and that rocket launcher is like one of the best and most reliable rocket to have for a very long time.
With your one brave whaler all you need are seagull missles and 2 more seagull launchers and that's gonna be enough to fight most opposition.
Yes you can't craft those missles and those are expensive but the conversion launcher
outranges enemy fighters (not viper fighter tho) and sentries!!!
Best solution to blast those 'crackdown'-sentries out of the sky with mere seagull missles. Other codexes have to use expensive stingray- and lancer-missles to fight/outrange those crafts.
Only disadvantage of seagulls is the mediocre damage. Those rockets are meant to gun down other fighters and medium-sized crafts with 0-10 armor value.
Cruisers, heavy freigthers and all those bulky large/huge ships will soak up the damage entirely. As long as you can't buy meteor-missles 1-2 hammerite launchers will do the best to chew through the health pool.
Use your tank/fighters to remove the shields first. Those don't benefit from the armor value of the ship. Once those are down, bring in the rockets to punch through and finish it off.