This looks very effective.
For sealing the base - I did a flocked mat using decorators caulking and impressing flock into it. I sprayed it with diluted PVA glue using a hand spray bottle from a gardening centre or wilko's. I also then used cheap hairspray as well. Belt and braces.
All I was looking to do was hold the flock in place, it didn't appear to darken it much although I didn't do a test piece so can't be sure.
The other alternative would be the army painter Matt varnish, a more expensive solution but probably better for you.
Please test first you don't want to ruin this nice piece.