Possible Solution
So you want better antenna performance in the car, but want your CP200 to return to service as a handheld quickly. The CP200 has a screw in type antenna jack, which would delay you somewhat. So I suggest the following:
1. Obtain an adapter like the following
BNC Antenna Test Adapter for Motorola Radio CP040 CP200: 001531-055 Virtual Village USA
this will convert your radio to a BNC antenna jack, which connects/disconnects quickly.
2. Get a simple mag mount or other mount antenna for your car, like a nice VHF broadband halfwave
since you don't specify the freq, but make sure the mount has a bnc connector (you can buy mounts with coax and bnc connectors installed on ebay).
3, Get a VHF rubber duck with a BNC for your handheld that is tuned to the correct frequency range you need, you might want to check out rfwiz.com.
So enroute, you quickly unhook the bnc ht antenna, hook into mobile antenna (it's a twist like a tylenol bottle). On scene, reverse the process. This approach will spare your HT, because the abuse of hooking unhooking will fall on the adapter not on the radio. Hooking/unhooking directly to the radio without an adapter is a likely path to rapidly breaking most radios.
JB