A j-pole antenna has a built in ground plane and works very well. Just
google on jpole or j-pole antenna. Or maybe a full wave loop if you
have the area for one. A dipole also can be used with up to a 90 degree
angle in the center. Just some ideas. Contact a local ham radio club. A
dipole with a 90 degree angle is fairly omni-directional and easy to
build.

Have the antenna checked BEFORE testing for SWR with an MFJ antenna
analyzer from a local ham club. The ARRL antenna handook for VHF is an
excellent resource.

I would definitely MAKE SURE the antenna cannot come loose. Use 50 ohm
coax to feed if that is what impedence the radio expects.

Rob