What's the best way to break my rig while towing?

Without detailed knowledge of your setup... the further up front and the lower the additional weight is distributed, the better it should be. You could also offset some of the weight by traveling with the fresh/gray/black water tanks as empty as possible.
You are probably already way over the stated payload of the truck - but you have done a number of modifications to address this. Only you know how your rig handles as it is today.