Forgive me for essentially remodelling your entire team, but I don't think either Gastrodon or Virizion will provide much coverage for your current team. Also, your HM slaves aren't complete (I don't know where you are in the game right now, so it's hard to tell).
I know this is an in game team, but that just means you need to rely on type advantages even more.
Pidgeot - only has 3 moves? It's also not a great bird/ flying Pokemon, because of low stats. It can also only learn 1 HM move
Meganium - has no attacking moves. I'm not too sure what it's even there for.
Lapras - okay, but Thunder and Blizzard only have 70% accuracy w/o weather, so not that great
Latias & Latios - I wouldn't have both on the same team. They're weak to the same things and cover the same things as well.
Judging from the fact your Pidgeot knows Heat Wave, I think you should be at Humilau because the move tutor for Heat Wave is there. Or maybe it just came with the move when you traded for it.
Pidgeot - Fly, Roost, Air Slash, Quick Attack
Meganium - Cut, Strength, Aromatherapy, Energy Ball
Lapras - Waterfall, Surf, Ice Beam, Toxic/ Frost Breath
Latias - Psychic, Recover, Dragon Pulse, Thunderbolt
So Latios is a bit unneeded.
Virizion isn't that good in light of your current team, because of its x4 Flying Weakness. You already have Meganium, so I would suggest another Fighting type.
Terrakion - Close Combat, Stone Edge/ Rock Slide, Earthquake, X-Scissor
Scrafty - Drain Punch, Crunch, Ice Punch, (filler move; Dual Chop maybe)
Chandelure - Flamethrower, Shadow Ball, Energy Ball, Confuse Ray