From the Link, I am familiar with Dive Deep Dogs work.
I have discussed the materials he uses to make a structure and know he likes a compressed Plywood referred to as MU 25.
My suggestion for a very effective and affordable Plinth would be to go on to Lenco Heaven forum and find 'Anwesh' who supplies Permali Board.
The next option would be Polybentonite Resin, much can be learnt about this on Lenco Heaven or the SP10 Thread on DIY Audio, where good guidance is offered for producing a mould to make the form of the Plinth.
Garrard-SME have stole the DIYers' Pb' Resin method and use a version of it on their $60K 301 TT.
https://pinkfishmedia.net/forum/threads/permali-panzerholz-help.274028/
https://www.garrardturntables.co.uk/301-advanced/