Antenna install on golf cart

[WSIM522]

I am new to gmrs, without a lot of technical knowledge. This winter i plan to install a gmrs mobile radio on a golf cart. Since the top and sides of the golf cart are NOT metal, I am bewildered concerning a mobile mounted ghost antenna needing a ground plane surface. Any suggestions or thoughts would be appreciated. 

I would be talking simplex to a base and other mobiles in a country setting. The mobiles will not connect to the nearest repeater, but the base does connect to the repeater.

[gortex2]

Rugged Radio makes a roll bar mount. Thats what I used on our gold cart originally. I since moved it to our sxs utility vehicle. Is it ideal. No. does it talk to the house and other radios on the farm. 

https://www.ruggedradios.com/products/antenna-bar-mount-for-horizontal-bar

They also sell a disc you can mount under it but I've not needed it in my application.

[BoxCar]

You can also put a small disc of steel to the top of your cart and use a mag mount antenna base.

Hillman 6-in x 18-in Cold Rolled Steel Solid Sheet Metal 11758 at Lowes.com

[WRUU653]

@gortex2 and @BoxCar both good suggestions. I like fabricating so I’d probably go the piece of metal route myself. You can even buy a disc with an 3/4 NMO hole already from Antenna Farm or they have this powder coated steel disc that has a sticky back to use with a mag mount.
They have Laird “no ground plane” antennas in the 450-750 MHz range also which might work well with the roll bar mount though I have no personal experience with them. 

[WRTC928]

I have a Diamond SG7900 "Super Gainer" on my truck. Although it isn't officially a "no ground plane" antenna, it works surprisingly well on GMRS, 2 meters, and 70 centimeters on the back end of the bed rail where there is essentially no ground plane. It has 6.45 dBd gain on GMRS and really blasts out a signal. It's a really tall antenna, though, and probably not the best choice for a golf cart. I've used mag mount antennas on a 16" pizza plate as "base" antennas and most of them work pretty well that way. In your case, I'd probably epoxy a piece of sheet steel to the top of the cart and use a mag mount. If you don't mind drilling a hole in the roof, aluminum works just as well as steel. I'm a big fan of the Comet 2x4SR. It does require a decent ground plane, but 16" seems to be enough. Bigger is better, if the roof of the golf cart is big enough to accommodate it.