RadioBanter - antenna for van

Hi all,
I'm a novice who needs some advice.

I've just purchased a Cobra 148 GTL to put in my Dodge RAM 1500
conversion van, and I'm having some trouble trying to figure out what
kind of antenna to mount on it.

I would have preferred a magnetic base as I don't want to advertise the
fact I have a CB on board, but as the only flat place to put it on is
the roof I figured that wouldn't be a decent option, not unless I want
to have the antenna smashed around everytime I go through a drive
through facility or car park! That or I mount a 1' antenna on the base!

A couple of CB shops have suggested different alternatives for using a
spring-mounted stainless steel whip antenna set up on the rear bumper.
Does this sound the best option?

As many of the people who frequent this forum obviously know their
stuff I wanted to ask if people here would like to make any suggestions
on which combination of base/spring/antenna would work best for me on
the van? If it helps any the comination would have to be over 54 inches
in height to clear the roof line.

One last point. As the top of the bumber has a plastic cover over the
steel I'll need to ground the unit through it. Is there a reccomended
way of doing this for an antenna?

Thanks in advance.....Tim