• A phone with resolution at least 840x1050px per eye(a bit less than half of a screen). I use Samsung S7.
  
• A holder for it: Google Cardboard or something more elaborate. I recommend going elaborate way for something which has lens assembly adjustments and is strong enough to withstand heat emanating from the phone. If you are a junkrat like me you can ducttape a fan powered from dedicated USB cord to it.
  
• Good and long USB cable. This is not mandatory, but I advice you to go that way to get the best experience possible from this setup.
  
• ...or a wifi router.
  
• A controlling device: controller or joystick. The rule of thumb: the more buttons on it - the better as you can't easily delve into the middle of keyboard with HMD on your face. Yes, some parts of keyboards like edges or special keys like space and enter are easily recognizable by touch, but it is not enough to cover all the vast control scheme of the game.
  
• The PC

Speaking about PC, I have no framedrops with this configuration:

• Processor: Intel(R) Core(TM) i5 CPU 750 @ 2.67GHz (4 CPUs), ~2.7GHz
  
• Memory: 16384MB RAM
  
• Video: NVIDIA GeForce GTX 750 Ti

It is below minimal spec but it gets the job done.

As fake HMDs don't have proximity sensor which tells the game when user has it off to switch between 2d and 3d mode there is official way of forsing it to always enabled state which is crucial part in making the whole thing work:

Option 1:
Start the game with commandline parameter "-openvr_force_proximity" (without the "")

Option 2:
Add the following line to the config.xml in the game-directory (somewhere inside the <root> block):
<openvr_force_proximity>true</openvr_force_proximity>

You need two things for that: TrinusVR Client on your phone and TrinusVR Server on your PC.
https://www.trinusvirtualreality.com/ is official TrinusVR website where you can download the server and find how to get client for your particular handheld device.

It is the easiest part and is mostly about setting you preferences:
Make sure your capture mode is set to SteamVR. This is crucial.
Compression: if you are planning to use tethered connection set it as on screenshot to ensure the most crisp visual experience.
Sensors is a tricky beast: setting deadzone solves the drift issues but makes headtracking completely unnatural and daunting. Using experimental antidrift helps me, but sometimes it still starts to drift and in that case the only option is to shake head violently to stop it doing that. I guess this is the price you should be paying for not having a proper HMD like Vive.
In general you will need to touch only two options here: IPD and Legacy Capture Mode. Switching capture mode is required when your 'HMD' phone displayes black instead of SteamVR 'lobby' or anything in general when you start. IPD should be configured once you launch SteamVR on the next step.

Caveat: I recommend setting center, rotation and sensor ignore to buttons far away from numbers as those are used by the game in the radial menu interaction.
Caveat 2: TrinusVR server doesn't register keyboard presses when there is other input device connected like controller or joystick.

No configuration is required except setting up tethering to the host PC. If you are okay with jpeg all over your eyes you can safely use wifi network, but with the low resolution of my Samsung S7 it was too much of a sacrifice. Yes, additional cable might be a problem so you should find something long enough, but capable to work with hispeed USB.

Your cellular network provider might be against the idea of setting tethering so you have two choices there:

• Change the network provider for good
  
• Install non-official android

This one is special because you may not need to do any configuration at all, but before you can decide if you need that it is still required to check actual virtual HMD resolution.

Open SteamVR menu and click Settings:
Select 'Developer' tab:
Look at supersampling option and check the 'Default' one. 840x1050 is resolution of virtual HMD, but this is too low for game to start. This step is important: adjust supersampling parameter to make the first number above 950 value.

To run the game:

• Make sure trinusvr triangle on a phone is purple
  
• Put the phone into holder
  
• Put the holder on a table in stable position and do not touch it
  
• Click on trinusvr triangle on a TrinusVR server software on the pc, it should state: "Trinus ready..."
  
• Run SteamVR. Wait for it to start and indicate 'Ready'
  
• (Only for first time) Wait 10 seconds, put HMD on, adjust IPD on TrinusVR Server, adjust lens assemblies if your holder supports physical adjustment. Put HMD back.
  
• Run the game. Wait for it to pass initial loading
  
• Put the HMD on. You are set!

And here is what this all about!

Now you can try to see it yourself and decide if you feel like getting HTC Vive, Oculus or if you find resolution of TrinusVR solution adequate to keep it that way.
Enjoy!