.htaccess url rewrite with filter

I'm trying to do some custom url rewriting with .htaccess file but I'm getting no luck.

We have a filter on the manufacturer page and when it changes it adds the category to the end of the url and gets the manufacturer products in that category, our current url looks like this:
https://www.domain.com/manufacturername?category=72

I would like the url to look like this:
https://www.domain.com/manufacturername-categoryname

I can't seem to figure out why it dosen't work (does a 404 error). Is it possible to do the above? How do you get the variable for category is it just a php get request? My htaccess code is below

RewriteBase /
RewriteRule sitemap.xml /index.php?route=feed/google_sitemap
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^([^?]*) index.php?_route_=$1 [L,QSA]

Code (markup):

 

I think mod rewrite is easier in this example as we have over 60 urls. Does anyone know how to do this?