All rental cars are off site of the airport. Find a shuttle and head over. It is a 5-10 minute shuttle ride. All the shuttles are going there. Once there this is the most streamlined car center I have been too. Find your agency and get in line. The rest falls into place.
On the return trip, there is a gas station on the way to the car center. Top off there. After drop off the shuttles are set to drop off at airport gates. So be sure you know what shuttle you are boarding. Some of the staff in that area are huffy and crabby so be ready to stand your ground.
I no longer do business with Enterprise due to the consistently crappy service out of the Milwaukee airport, lack of upgrades and anything helpful from that team after 4 straight months of rentals. Just had a bunch of points to get rid of.
The Vegas team was top notch. If I was doing business in that area I would reconsider.