Future War Commander.
Or you get any version of epic 40k and adapt it for your vehicles of choice.
Yeah, these would be my choices personally.
Also, a quick note on Epic; the third edition rules are pretty easy and cheap to find on eBay (split across three small A5-format books in total: "Rules", Armies", and "Battles"), and despite the mixed response from the wider gaming community, I have found them to be an
excellent set of rules - fast to play, lots of manoeuvring, and has a reasonable mix of small and large scale detail.
The only big tweak I think they need is for units to have a separate firefight value added to their statline. This is because outside of movement, there are three main fighting phases in the game; shooting, close combat, and firefights (which are very close-range shooting engagements, each of which is meant to represent a game of full-sized 40k!).
This is because shooting and firefights use the same stat (Firepower), and so this means that units which are good at shooting dominate too much in 2/3 combat phases of the game. Splitting this stat means that units like flamethrower tanks can still be good at firefights, but are now poorer in the shooting phase. An easy way to do this is to show a unit's Firepower value as a split stat, say "1/3" - this means that you get 1 Firepower for shooting, and 3 Firepower for firefighting for example. Since you will likely be making some stats to suit your model collection, this would be an easy thing to incorporate.
In any case, the rules are solid structurally, and you can also add things like further unit special abilities quite easily if you want to.