There's really only the one FBO there at KSGU, Above View, nice facility, call them to set up rental cars. East side of the field. I believe the hangars, etc. on the west side, shown on airport diagram, are only for resident aircraft, no services over there.
Don't try the old airport, ababdoned, further west. I think there's a youtube vid of someone doing that a couple years ago!!
Where are you going while there? You could check out the (much) smaller Stout Field at Hurricane, 1L8, if your goal is Zion. I think they even have rental cars there, but I've never landed there.