If you’re looking to do a similar basing scheme, here’s what I did:
vallejo terrain paste stuff (forget the name)
various cheap sands and rocks applied with PVA on top
50/50 pva and what applied to the sand after it dries
vallejo air anthrocite grey base coat
vallejo air stonewall grey in patches
Vallejo Air Light Sea Blue with the Stonewall Grey in more patches
vallejo air dead white in even more patches
the tufts are army painter winter (can’t remember the name) with some white drybrushed over them.
the directional arrow and slots were just a layer or two of P3 Frostbite applied with a brush after everything.
black paint around base rim
**I’ve painted my miniatures first here and wish I hadn’t. It is much faster and cleaner to first get as much basing done as possible**
I paid special attention to ultimately keeping the base slots as clean of texturing elements as possible – the blunt end of tweezers were helpful for scraping off stray basing material without gouging the plastic too much. The WIP photo below is before cleaning and shows all the sand, etc. you don’t want sticking around in the base slots. I didn’t paint the individual miniature base rims black as I really wanted to try and have the smoothest possible transition between minis and tray basing.
I used an airbrush, but i’m sure a brush could produce similar results with little effort.
Another tutorial I highly suggest can be found here!