WD-40 is a water displacement compound and is a very poor penetrant. Kroil or PB Blaster are both excellant penetrating fluids and they will help tremendously in applications like this.

Are you using sockets with a long breaker bar? You need as much mechanical advantage as possible.

If you are referring to the rear trailing arm bushings getting the bolts out is minor compared to removing and installing the new bushings. The rear trailing arm bushings are the ones that are actually pressed into the brackets that are attached to the axle housings. It takes a specific tool to remove and install these bushings and they can be a real problem sometimes. I can not advise you on how to proceed as I do not know your particular skill level.

Randy