so ive been running a Tram 1185 dual band on a trunk lip mount for about two years now and its been fine, decent signals into the local repeaters, no real complaints. but a buddy of mine keeps telling me i should just go mag mount on the roof and be done with it. his argument is the ground plane on a trunk lip is garbage compared to a full roof mount.

thing is i dont really want to mess with drilling or anything permanent and the mag mount seems like itd scratch up the roof over time if i leave it on there. plus i commute on the highway and honestly a little worried about it at 75mph even with a good magnet. have had a whip antenna on a mag mount fly off a different vehicle years ago, wasnt fun.

anyway the question is does the ground plane difference actually matter enough to hear in practice, like on 2m, or is this one of those theoretical things that only shows up on a spectrum analyzer? currently running a 50w rig so its not like im at qrp levels where every db counts.

honestly for 2m into local repeaters with 50 watts youre probably not gonna notice much difference. the repeaters arent that far and you've got plenty of power. now if you were doing simplex over longer distances or trying to hit a far away machine on 70cm it might matter more. trunk lip mounts do have a compromised ground plane but the antenna still works, its not like youre running a rubber duck.

the mag mount scratching thing is real by the way, i put a thin microfiber cloth under mine and it helped but still left some swirl marks after a year. if youre staying put id just leave the trunk lip alone tbh, two years with no complaints is a pretty good track record

the roof center is genuinely better for pattern, you get a cleaner omni vs the trunk lip which skews things a bit toward the rear of the car. whether you can actually tell depends a lot on terrain and what youre doing. i ran a NMO mount on the roof of my last truck, drilled a proper hole, and yeah it was noticeably cleaner on 70cm especially. but that was a permanent install and i knew i was keeping that truck.

for a commuter car i wouldnt bother drilling. the mag mount speed concern is real too, ive seen people lose them. get a mount with a strong magnet and keep an eye on it but a roof center mag at highway speeds should be ok if the base is solid. the Tram youve got is a decent antenna anyway, dont overthink it