Thank you --weezl-- for covering some bases there, I was about ready to hit my head against something hard.
Fiberglass CB antennas are not whip antennas, they are fiberglass antennas. Whip antennas are the longer steel antennas (4, 6 and 8' and the like), because they are VERY flexible and will "whip."
Years ago I almost put 4' fiberglass antennas on my Ranger. I wanted to put one on each side of the cab and figured it would look balanced and cool. Except when I started learning about CB setups, I discovered that one antenna would have to be just for looks because if both were powered, it would cause a lot of interference, thus reducing my range considerably. IIRC, the minimum distance between two antennas is around 8 or 9', which cannot be achieved without hanging them off to the side of even a fullsize truck. Also, I found that even with base springs, fiberglass antennas are not ment to be used where you will hit overhead obstructions - like garage doors or trees - because there is a risk of breaking them.
You cannot cut down a fiberglass antenna - it will ruin the SWR and run a risk of blowing out your finals the first time you key the mike.
Setting them low in a bed reduces range considerably. Ideally you want the tallest, longest antenna you can use. And Ideally you want the antenna placed either in the center of the vehicle (for maximum range in all directions) or in the back passenger side corner of the vehicle to give you maximum range in the forward plane and to the left (thus you can really reach out to opposing traffic on a highway to get news on weather and traffic conditions in plenty of time to find an exit).
I run a 102" whip on my choptop, mounted it to the top of the spare tire carrier (which puts the tip of it about 14' in the air). I love it and have an extra 102" whip waiting for me to pick something to mount it on. I've been thinking of putting a CB in my F-150, but haven't decided on running the big whip or something shorter.
As far as the OP's questions....
No, do not cut them.
Bending them causes damage. Remove them or get a mount for them that will allow them to be removed or pivoted out of the way.
Or, get a steel whip antenna.
You can pick up a cheap SWR meter from like Radio Shack or online for under $30 and it's good enough for the average user.