so ive been running a 5/8 wave collinear on a mag mount for about a year now on my F-250 and honestly the mag mount works fine but i keep reading that a proper NMO through the roof is the right way to do it. my concern is obviously the hole, i dont want rust issues years down the road and i also drive in some seriously bad weather up here so sealing it properly matters a lot to me.

the other option ive been thinking about is a fender mount, drill into the fender instead of the roof. less gain headache since the antenna isnt centered on the roof but i feel like for local repeater work and some simplex it probably doesnt matter. anyone gone the fender route and regret it or is it fine for everyday use? also wondering if there's a noticeable difference on 70cm specifically since the antenna pattern would be more off-center on the vehicle.

running a TM-V71A if that matters, mostly 2m and 70cm.

done both on different rigs. honestly the roof NMO is the way to go if you can stomach the hole, the radiation pattern is way better being centered on the ground plane and you do notice it on 70cm especially, you're right about that. for sealing i used Sikaflex around the mount body and have had zero rust issues after 6 years on my tacoma, the NMO mount itself has a rubber gasket but i wouldn't rely on that alone.

the fender mount works okay for 2m repeater stuff, wont lie, but i had one on an old jeep and the pattern was noticeably worse off the side the antenna was on. people on the other side of the repeater would sometimes comment on my signal being a bit ragged. could have been other things but i switched to roof and it went away. if you're just hitting local repeaters and dont care about squeezing every db out of it, fender is fine and a lot less commitment.

i went fender on my silverado and havent had any complaints, been on it for maybe two years. does the job for everything i do which is mostly driving around chatting on the local 146.something repeater. i think people overthink the ground plane stuff for just casual use. that said i did not do a great job sealing mine and now im a little worried about it lol, might redo it this summer with some proper sealant. the NMO mount i used was a Larsen and it seems solid.