Normally, applying basing material is the last thing I do on a miniature. I use a product from Liquitex that's acrylic, making it durable, already has grit to it, and after I mix pigment to it, halfway done at application.
I wanted a more rocky texture to these bases so they looked like they were wading through rubble. My skirmish miniatures are always based on steel washers. I like the look of the thinner bases, and as I line my transport boxes with magnetic sheets, it keeps them from falling over or shifting. Granted, the walk from my storage room to the game room is about 20 feet, but they occasionally they take a longer trip.
I used tacky glue liberally apllied. Then used railroad tallus (sp?). I started using sand, but it was too fine, and switched to rubber in-fill for the final part. My wife used to work for an artificial turf company and I have not only a garage full of turf samples, but 5 gallon buckets of sand and rubber in-fill (the black rubbery stuff in the "grass" that keeps it up). Don't know how it will hold up to paint, but here goes nothing.
Also note, I had to use "greenstuff" to hold the heads on. Superglue wasn't getting enough of a purchase.