Park my bike a decent distant away (with full ammo bags) and then use the Chicago Chopper + RPD and just kill them running back to my bike to resupply. Never had to use bombs or traps in any horde I took down including big ones like the sawmill horde as I always had enough ammo.
What difficulty? They won't allow me to leave Hard mode, I started a nornal save and I'm half way back to where I am on hard which is the sawmill but keep funding myself booting up the hard save even though they are near impossible without taling them out in chunk and then farming, rinse and repeat.
Everything in the above reply is my opinion, from my own perspective and not representative of reality outside of my own head!
-Android user, please be gentle with critique on my spelling.