Being divider-less might mean you can't stack the rock quite as high without it tumbling down near the skimmer, but it's still doable (I had a sump like that once). Pick a return pump and protein skimmer that fit your height constraints for the room underneath the tank and then see how much rock you can fit on the other side of the sump without it interfering with the skimmer and return pump's inlets. You'll want both pieces of equipment to be easily accessible without rocks in the way when the need for maintenance arises. Depending on what fish species you want to keep, it's often still good to have a decent amount of rock in tank to help form hiding spots, territories, and/or grazing areas for fish like tangs.
The skimmer should remove the need to run chemical media, so after that you'd just need some circulation pumps for the main tank.