You obviously have some navigation skills if you have your ppl. You say you're not worried about your navigation as such, but have difficulty in pin pointing your position on a very local basis.
I think we all have problems locating and identifing small airfields and vrp's that we haven't been to before, so don't be too concerned about that.
Personally I recently got a gps unit, and program my route into it, turn it on when i go flying, and then put it aside, and proceed with my plog and map. Like you I enjoy the challenge of navigation.
However the time comes when I expect to be over a town, and all that I'm over is a small collection of buildings. I believe I'm over the correct place, and continue to the next point but at the same time thinking what if that was the wrong town, then where would I be now? A quick glance at the GPS would confirm if I'd made the correct assumption, and put my mind at ease and reduce the mental calculations. I've found that it has not improved my navigation, as there was nothing wrong with it, but it has improved my confidence in my navigation. It's great to be able to check it, if you are in doubt, but I wouldn't follow the little line if I was you. You'll only lose your confidence in your navigaton.
As for an aerial, you can buy ones that stick to the window with a suction pad. I have only used my gps for a small number of flights, but haven't had a problem with losing the signal once this aerial is connected.
Hope that helps.
dp