I have a stern mounted vhf antenna. Not sure of the specs, but it's one of those fiberglass jobs you see for about $50.
Length of cable and number of coax connections can degrade transmission strength. And having an antenna atop the mast can be a problem too. I don't like to go aloft too often for maintenance, but as a trailer sailor you don't have that issue. But as a safety issue, it would be a bummer to be dismasted and have no vhf.
My vhf works very well and I've easily conversed with the CG 20 miles offshore, but as Bill says their antennas are pretty high up.
Gemini Catamaran Split Decision