I have a version of the XAE with modular tanks, where you build a chassis, add a cannon (I think it makes more sense to use aircraft weapons, since in vanilla it is those that unlock the HWPs) and a few components, to get your working tank.
If you go that route, it is good to also have disassembly projects that allow you to recover the weapon, chassis and component, so you can remove one turret and add a different one. I decided that a tank wreck could be repaired into a chassis, but that the extra components and weapon(s) would be lost.
Also, if you want tanks with two weapons, it starts creating a LOT of assembly and disassembly projects.
I've attached my rulesets if you want to use them to get started on the full tank building project.