Ground cover

No experience with that product, but my system is to either fill the seam with a joint-type compound and smooth over with a putty knife (I use a flexible vinyl compound available at the big box stores so it doesn't crack) or simply tape over the seam with duct tape.

In both cases, just apply some adhesive to the area (spray adhesive works) and sprinkle with Woodland Scenics fine turf which comes in a variety of colors. 

  I’ve seen a lot modelers using what’s called Ground Goop over foam.  Modeler Lou Sassi came up with the mix. Nothing you can buy. But easy enough to make and pretty economical.  If you do a Google search you can come up with a lot of different recipes. There’s  also numerous You Tube videos on mixing and applying it.  It’s basically converting Latex paint into a spreadable paste. You find something close as to what the base color is of your scenery. Before it dries and sets. You can place your basic ground cover over it. In your case. You could place your scenery base right over it to give it some texture.

I use blue painter's tape over the seams. Then I paint using WS Earth Undercoating.. I like the variation in color and am ok with patches of dirt showing through like in the real world. But you could use regular flat brown paint. Michaels, Hobby Lobby etc. also carry cheap landscaping stuff. WS is a little pricey but sometime worth it. I also use real sand, pea gravel, and have used some Paver Filler, it's like a mastic but colored. Oh, and real dirt, sifted done and the clods separated to be used as needed.

I covered the seams of the foam board with duct tape and then painted the whole thing with brown paint (dirt).  Then used watered down elmers glue to apply all the different ground coverings.