I'm planning on running a narrative campaign with my partner which is loosely set in the 40k universe (set within a custom star system which is mostly isolated from the Imperium).
I've been looking for a set of rules which can handle small skirmishes and occasionally the odd vehicle or two, but haven't found anything perfect yet. For this game we tried using a modified set of Frostgrave rules (to allow for squads) , but found it wasn't ideal for a number of reasons, so I think I'll try Gates of Antares next time and see if that fits.
Here's some pics of the board setup. A Planetary Defence Force base had been taken over by Renegades calling themselves the Echeni. The surviving PDF troopers retreated and later mounted a counter-attack, their objective was to steal a shuttlecraft and use it to warn other PDF forces about the Echeni threat.