Hi! Just wanted to mention a few things as someone who really likes using Trick Room. These are general thoughts though and not advice for Erick.
ABOUT TR SETTERS
As mentioned, Oranguru is one of the only three setters in Rejuvenation right now. (And probably the only viable one.) You can get Smeargle a little bit after Erick's gym and that can learn Trick Room via Sketch. I'm not entirely sure of Smeargle's viability though.
If you're hard set on TR, your other option is to have two Orangurus.
Another recommendation is to have a hybrid team where you have a "trick room" mode and a Pokemon or two as back-up when Trick Room is down, and you're not able to set it up.
POKEMON RECOMMENDATIONS
Follow Me/Rage Powder support: In doubles, there are times where you want to draw all the aggro away from Oranguru, especially if you're in a situation where both enemy Pokemon can K.O. Oranguru. It also creates opportunities for set-up. Amoongus (Rage Powder), Butterfree (Rage Powder), Vivillon (Rage Powder), and Pachirisu (Follow Me) are options that come to mind. I would recommend Indeedee to create a Psychic Terrain core too, but I think there's a bug right now where it only learns the male Indeedee moveset.
Oranguru: I'd recommend having another Oranguru or making room for Instruct in doubles, especially if you're running Eruption/Water Spout/Blizzard related strats. If you decide to make room for Instruct in the Oranguru you currently have, I'd drop Calm Mind. It's not a fast enough boost to really matter. In trick room, every turn counts, especially since the only way to extend TR turns is for it to hold an Amplified Rock, and there are times where you'd rather have it hold a berry or a seed.
Special Coverage: You're lacking in special coverage. To be fair, slow special attackers aren't that common, but here are a few to consider:
Torkoal: Slow sun setter with Eruption.
Abomasnow: As mentioned by Cyphre, Blizzard spam is powerful. Plus, in Erick's battle, you can freeze the field with it. You also lack ground resist, and being part grass type, this could be a decent option for a ground resist.
The electric types mentioned by Cyphre are good options too. Lapras is actually really nice with that No Guard Sing Utility. If anything, I'm more inclined to drop Milotic. I don't think it really hits hard enough to really justify using it besides as an anti-Fairy Pokemon, and it needs Coil for it to be really threatening. If you're looking to cover an Anti-Fairy niche, there's Perserker who gets Fake Out and is a Steel type.
Crawdaunt: If you can, I think you should breed Aqua Jet onto Crawdaunt. STAB priority is nice, especially when Trick Room expires.
A-Marowak: If you can find a Thick Club, Alolan Marowak is also a good option as a Trick Room attacker. Besides that recommendation, Cyphre's recommendations are good as well.
Healing Wish: This is more of a tech option to consider having in your PC box. Healing Wish is nice in certain situations where everything goes wrong. You can fully heal a Pokemon you have in the back when you can't set up TR again or you can use it to heal and pivot into your TR setter. Lopunny and G-Rapidash are the users that come to mind, but for a full list, you can check serebii or bulbapedia.