Valks and certing up ammunition belts seems to be ideal as well. Between flyby ammo restocks and the fact that HAs, engies and infiltrators will probably be the only ones flying in them, they make a bit of sense. 111 certs to turn into a flying gun emplacement of doom (well, of paper-mache armoured doom) sounds like a good deal. 3 extra magazines is a fair bit of leeway when it comes to firing at will.
It'll give you a bit more sustain and a lack of care as you randomly fire at anything your pilot gets you near to. With mana turret/ammo pack waystation flybys to top you up when needed. It might be a little bit of a passive way to play, but sometimes that's fun as well. Just a pointy-clicky shooter.
It'll also give you something fun to do when you've only got a couple of mates online and you just want to rumble seat grumble or talk while not really doing much. Go valking. Point, click, crap on. You're still contributing, but you can probably watch a twitch stream while you're doing it
edit: For more serious play, two heavies with lvl 2 belts isn't really that bad for 550 certs (the max for HAs). 2 extra rockets and clips goes a long way to add to the damage output. A total of 14 rockets (or whatever ES weapon equivalent) and shit-tonnes of ammo for a LMG/ES HA weapon is pretty nice for a gunship with 2 HA rumblers. Add a rocket pod front turret to it with max ammo certing and even without an ammo supply dump you're in business.
edit 2: Actually, if pilot -> rumble seat swapping is a thing, especially without needing a spare seat (gunner), then a group of 4 heavies in a valk makes total sense. As long as all of them can pilot it a bit. Heaps of ammo, some AT or AA potential, and almost perfect resource usage. 250 nanites for each valk, but any HA can pull one. As long as any valk you pull manages to last a minute, and one of them two minutes, they're essentially free. Depends on cooldown for the pull, but 4 valks should last at least 5 minutes. Especially with 4 HAs of seat-swapping firepower coming out of them. Free on nanites, and fun-with-a-flying-gun-platform for 4 people. Essentially indefinitely.