Input on NGP 2m 1/4 wave antennas?
Yeah--they don't exist. By definition, a 1/4-wave antenna requires a ground plane. Well, okay, I guess that's not entirely correct. You
can run a 1/4-wave antenna without a ground plane, but its performance will be substantially compromised. This is why antenna manufacturers tell you a 1/4-wave antenna requires a suitable ground plane for proper operation... but it looks like you already know that.
What do you do if you don't have a suitable ground plane? Use a 1/2-wave design instead. They are extremely forgiving when installed without a ground plane, and still perform very well. This is one more reason why I'm such a fan of the Larsen NMO2/70B antenna.
Do you think you can find/make room for that antenna on your rig? Somewhere? Anywhere?