so ive been trying to sort out the best place to mount an antenna on my truck for 2m/70cm and honestly its been more frustrating than i expected. i picked up a used Yaesu FTM-400 a few months back and its been great in the house on the desk but i want to get it actually mobile finally.

the problem is my truck has a fiberglass bed cap/topper thing and a bunch of roof rails so finding a clean mount spot is tricky. ive seen people do lip mounts on the trunk edge but thats on sedans usually. i was thinking maybe a hatch mount on the back of the topper but then im worried about the coax run and ground plane issues since fiberglass is obviously not grounded.

anyone run into this with a truck cap situation? wondering if a mag mount on the roof of the topper would even work at all or if id just be wasting my time. the radio itself is already mounted under the dash and wired to the battery so thats the easy part i guess

yeah the fiberglass cap thing is a real headache for ground plane. mag mount wont work well at all on fiberglass, the magnet part is fine but you lose the counterpoise basically and your SWR will be all over the place. what most people do in that situation is either run a NMO mount through the metal roof of the cab itself if you can get to it, or use a fold-down mirror mount on the side. mirror mounts arent perfect but they at least give you some metal to work against.

ive also seen guys fab up a small aluminum plate inside the topper and mount the antenna through that plus bond it to the frame with a grounding strap. bit more work but its a proper installation. for 2m and 70cm your ground plane doesnt need to be huge but it needs to be something. a quarter wave on 2m is only like 19 inches so a decent plate works fine.

i had almost this exact same setup on my old Tacoma with a leer cap. ended up doing a lip mount on the cab itself right at the rear edge of the cab roof and running the coax through the back window weatherstripping — not the prettiest but it worked great for years and SWR was solid. the FTM-400 is a great radio btw, the APRS built in is really handy once you get it dialed in on the road