There is plenty of space within the rules for custom missions involving vehicles. More work you put in the better it will be.
Also, When introducing tanks(rather than APCs) I find A full city board helps a lot. Enabling foot units to move around more, and giving movement restrictions to a tank adds a lot tot he game.
Narrative for vehicles i think is the best way to go.
Creating missions with no go zones, But with risk.
Last stand, with a unknown convoy moving though a city to pick up important Intel or stolen goods.
Drop mission into hot zone, with anti air weapons. Forcing a player to make a choice on position to drop.
Then complete a mission and then get out on the Drop vehicle they come in on.
Can be fun for a player to have to decide how long they can have a drop ship or APC sitting there under fire. To complete the mission. And the chance it all goes pear shape. Turning it into a last stand battle
Really there is no limit. One of the first ones we did, was a bunch of
IG having to repair a broken chimera why small group of Tyranids try and eat them.
With choice of what they repair first, Weapon, engine, or tracks.