Me and my friend are looking to make an off road go kart out of an old junker car. I'm wondering if it's safe to trim body panels on a unibody. For example, trimming the fenders, but not actually removing them to make room for different tires. Is this safe or should I look for a body on frame car or regular frame?
Look for a car with frame.
The guys from Roadkill turned a 1985 C4 corvette into a go-kart, and in one of their episode they even went off-road, but they installed a frame and roll cage etc and other safety gear. and have big budget and more or less know what they're doing. If you're going to attempt this, start with a car that has a good frame.
You’d want to have some engineering experience or worked in a body shop, before you start cutting car panels.