Larsen makes a couple of dual band antennas with NMO mounts that will make life easier.
The NMO mounts will give you the option of changing out mounts/antennas a lot easier. Maybe the Tram has an NMO, not sure, but after looking at some of their antennas at trade shows, I'm not impressed.
LARSEN NMO-2/70SH
Higher gain model:
http://www.theantennafarm.com/catalog/larsen-nmo2-70b-1712.html
NMO Magnetic Mount:
http://www.theantennafarm.com/catalog/larsen-nmommrpl-1097.html
Stay away from the consumer/amateur radio grade stuff. The slight cost savings isn't going to do you any favors in the long run. A name brand antenna like Larsen will last a long time if you look after it.
A good upgrade would be to ditch the magnetic mount and drill the hole. Getting the antenna properly mounted with a good ground plane underneath it will help performance. Also, using -just- the amount of coax cable you need will help a tiny bit, too.