VHF Antenna lengths

[Tarpun]

VHF is line of sight. All things being equal the taller the more range. Most 8' VHF antennas such as Digital and Shakespeare are 6DB gain which is the generally recommended max gain for smaller boats. Too much gain can cause problems in rough seas due to the compressed transmission band.
You shouldn't have any problem while trailering with the antenna laid down. Probably less stress on it and the mount than if you running with it up in a big sea. Securing it lightly with a bungee will keep it from bouncing up & down.
Get a premium antenna, Shakesspeare 5225XP or Digital 529, they do perform better than the cheepies. Dave