or, if you don't mind a weird look to it, you could just give the jeep tank tires, and a higher maxwheelspeed. it LOOKS like a hovercar, but isn't. just invisible tires.
that's how all hover cars work, i think
hover cars float! here is a pic of a hover carhttp://www.google.com/imgres?imgurl=http://www.deviantart.com/download/92758863/Hover_Car_Rolls_Royce_Phantom_by_DannyPCarlyon.png&imgrefurl=http://dannypcarlyon.deviantart.com/art/Hover-Car-Rolls-Royce-Phantom-92758863&usg=__lGEE2Ltpl-9TgOQ6FRTRWXOLpxs=&h=768&w=1024&sz=541&hl=en&start=0&sig2=Q7TkRQUIZ2RrPQ5bsjHT3w&zoom=1&tbnid=M0MuJpgDkLEU1M:&tbnh=166&tbnw=221&ei=ttSoTNS3JcP38Aa1uNCsDA&prev=/images%3Fq%3Dhover%2Bcar%26hl%3Den%26biw%3D1680%26bih%3D869%26gbv%3D2%26tbs%3Disch:1&itbs=1&iact=rc&dur=298&oei=mNSoTOexN8H38Aa2ksi0DA&esq=4&page=1&ndsp=25&ved=1t:429,r:3,s:0&tx=123&ty=59