As I understand it, the handheld antennas are for handheld radios, in that they have a BNC connector. At the least, you'd want one of the adaptors to accomodate the SO239 on whichever CB you have.
You might not get much of a range with the handheld antenna, either.
If size is the issue, I use an Atom antenna on the bike, with an EGP mount and I get a good 10 miles from that when I'm out and about.
our sponsors do a mount for transferring a h/held bnc fitting antenna to the window will not get a far a a full range antenna but will work better than on top of the set
For my Midland 42 Handheld i use a N type to SO239 adaptor , With this i can connect any Magmount Antenna combination to my handheld and get great range but the antennas do draw high power from the handhelds causing them to get hot if u are modging continually so best to switch to low power when running in convoy .
N type to SO239
If your radio has BNC connection use
this BNC to SO239
the midland 42 uses the bnc type mount cant see for the life of me how the n type comes into this if its running that fot the it sounds like the swr is slightly out but it will get warm with a lot of use
I do apollogise ,its been so long since i used it that i had forgoten that mine was the Radioshack TRC-1015 80 Channel handheld not the midland , they do look very similar but as you say the Midland 42 is BNC and it is the Radioshack / Maycom handhelds that are N type connection . The handhelds put out allmost 4 wats when used with the car adaptor as they get 13.8 volts as apposed to 12 volts from the internal batterys and this i think is why they get hot when used a lot with an external antenna .
i would give up on the window mount antennas found some where where they sell them GlobeTrotter & they no good to be blunt unless you only need it for a convoy as you will only reach 3 miles if your lucky but if your driving a GlobeTrotter cab i have seen GlobeTrotters with a mag mount on the rear with some thing like a 3/8 swivel adaptor attached to it with the antenna attached to the swivel adaptor,
or you just could get a gutter mount & bang it on to the rear as many truckers do & here is a link for you to choose what any antenna you would like from small to medium or large.