I recently tested this and got everything working except that the penetrator on the exit portal is fully visible at all times. I assume the "Invisible Barrier" is supposed to hide it, but it doesn't. I suspect I gotta look into rendering order since I believe that's how it's supposed to be hidden. Additionally I dont know why there's two Parent Constraints for each hand. I ended up putting them in the same location.
I've added self-deleting references to aid portal placement, fixed the sps depth detection (it was set to meters and should be plugs instead, with -0.95 to 0) and auto-parented the constraints. It also seems that specific positions (head ones) don't automatically impose specific setups on the handle (if this is broken animations or an oversight, I've yet to verify) - but I'll look into this shortly and give it a fix. I'd also be happy to help you add a better guide afterwards.
Once I fixed/optimized this, would you (Rain Jur) be interested in the package (free for you to use and redistribute of course)?
TL;DR: This works, but at the current stage requires expert knowledge in vcc unity.
For those in trouble with the current version:
Copy the folder to your project. Open the scene, copy the objects to your own scene and place them in your avatar. Add a Penetrator in the correct parent (location is mentioned in the readme). For this, I suggest to start with a mesh with no physbones to get your bearings. Set the Parent Constraint on the penetrators parent folder to Out and adjust your penetrators location so that it sits correctly on the portal. Set it back to In to restore its default state. (You probably need to set up the meshs rendering correctly to be hidden. If you read above, you know that I currently have not fixed this myself.)
Add vrcf "Armature Link" to each parent constraint and assign them correspondingly (Hips/Head/Left Hand/Right Hand).
(If you need visual aid: copy the Ex object and parent it into a newly created reference folder. Change its materials to something translucent. Add a scale constraint and target the Parent of Ex, "Containers". Dont forget activating the scale constraints. Add a vrcf "Delete During Upload" to it as well so your reference will get deleted on upload and during play mode. Scale Ex's "Containers" Parent folder. You can reapeat this for the En one to create a reference for your Portal Base one.)
Scale "Containers" to fit your avatar (if you created reference correctly, they scale with this). Move the Parent Constraints to the correct locations. For the hands (if symmetrical) you can copy your Transforms Position after adjusting it for one hand and flip x (+ / - ) to easily place the other hand. Go to the En-Portal folder and select "Oriface_Hole". Set the SPS Sockets Range Units to Plugs and have the range be -0.95 to 0.
This should set up most of it. Some things aren't working correctly on my end yet, but it'd become a bit elaborate if I started explaing now how you fix the FX layers and Parameters.