We use Mepitel dressings.
http://www.directmedicalinc.com/wound/mepitel.html It lays directly on the road rash, and can remain for up to 7 days. You cover with dry guaze. Daily you remove the dry gauze (more frequently if there's a large amount of drainage). Cleanse with normal saline, blot dry, but leave the Mepitel on.
It seems to work very well.
I'm also a fan of leaving it open to air to dry if it's not too deep or draining.