Ok, so I figured it was time to go lay out a new team custom-made for double battling and this is what I came up with. Any feedback is welcome; this layout (particularly EV spreads) is a bit of a rough draft.
Arcanine @ Heat Rock, Sassy
200 HP, 80 SpA, 54 Def, 54 SpD
So this is going to be a sun team for reasons we'll see in a second; bulky water types will also be a bit crippled. Arcanine's balanced stats mean I can use Flamethrower for STAB and Extremespeed for priority; Helping Hand should be very useful to support the other lead, Porygon-Z. EV spread on this guy is a total crapshoot at this point; I like the natural balance he has and I wanted to preserve that to some degree. HP is emphasized to increase bulk and maybe allow an extra turn of Helping Hand.
Porygon-Z @ Expert Belt, Modest
252 SpA, 252 Spe, 4 HP
Arcanine really sets up well to support this Porygon. Sunny Day allows SolarBeam to be used with impunity (and a lot of power), Tri Attack is the STAB move and is powered up by Adaptability, and both Ice Beam and Signal Beam provide type coverage and make it so that I won't necessarily have to switch him out right away to get a good match up. Expert Belt is used because his moves will be highly targeted and can use that boost well. The major danger, obviously, is Fighting type pokemon, and my bench reflects that.
Dusknoir @ Leftovers, Jolly
252 Atk, 252 HP, 4 Spe
Dusknoir is my general-purpose answer to Fighting types. I needed Ground-type coverage on this team and he, with high attack, can use Earthquake, which made him the Ghost of choice. I considered Golurk but the added bulk of Dusknoir won me over. Shadow Punch and Brick Break provide both STAB and coverage, respectively, and Destiny Bond is, to me, an under-handed way to earn a kill of a tough pokemon (not gonna argue with that).
Braviary @ Cell Battery, Jolly
252 Atk, 252 Spe, 4 HP
Braviary provides my last bit of coverage. Flying has always been one of my favorite types and I felt as though I needed one. It was either Braviary or Staraptor and I went with Braviary because of the slightly better overall stats. EV'd to be a straight-up sweeper. I added Tailwind to the set to help aid Dusknoir a bit (since I figure they'll end up together a decent amount) but that could end up making Arcanine/Porygon quite nasty to deal with as well. Giga Impact is the one move I'm torn about... The power (since it's STAB too) is amazing but I don't know how I feel about the turn skip. The presence of a teammate might offset that though. Cell Battery is a creative item choice which struck me as an interesting way to punish anything that tries to use electricity on Braviary.
Let me know what you think. If there are glaring holes I'm missing I need to know before I go breed this team haha. Any alternate recommendations for moves, items, EVs, etc are also more than welcome.