New springs or air bags

I have a 2001 prerunner that needs spring replacement. I want to install air bags so that I can tow a small camp trailer. Do I need to replace the springs or will just installing the air bags take care of both issues

 

Why do your leafs need replacing?

Air bags just help level the rear when under load, so if the rear is already sagging because the leafs are worn out then replace the leafs

 

With all due respect OP, the forum can help you better in one thread than two or more.

On to business

This. If your springs need replacing, they need replacing. Then add the air bags for the trailer.