you can do it without supports, it will actually come out much better. i will recommend a Large brim on the base i use a 6mm brim to make sure the body stays flat on the bed. my first tests were no brim and the corners were pulling up and bad warp-age started to occur
my first tests of the body were done with supports and they caused more trouble then they solved.
first get a bridge torture test STL so you can fine tune your printer and cooling needed.figure out the temperature for the material you are using
to get best results. i used hatchbox PLA at 205C with cooling 85-100% i run in an enclosure to help with layer bonding and shrinkage
here is one of my bodies running
you also do need to add a 100% fill layer where specified on the thing details readme. you have to go into the slicer software and force a 100% fill layer just under the grill for the front and just before the tailgate starts on the rear this is so the details have an attachment point for the bridging required. this is to keep the body shell as light as possible. you can also add 100% or higher fill areas using advanced slicer software settings to re-enforce areas around the body mounts or the roll cage.
i have 3 completed bodies under my belt and 2 tests i did for the front part that didn't work 100%