To cut the wheel wells, which has worked well for me, I use an x-acto knife and make an insision on the outside, but not all the way through. Make sure that you follow it out to the end of the lexan. Use sissors to start the cut, and then just pull the lexan away, along the cut.

The lexan will rip away just perfectly along the cut line that you made. If you need to do some minor cutting, I always use a dremel/sanding part to make the changes.

URC