Firestone ride-ride air suspension kit with 6-in lift

I just purchased a new 30-ft trailer, my truck sags a bit so I purchased the Firestone ride right air leveling kit! However looks like I may need a spacer under the bags! Any idea on which size? I'm kind of unsure...
Truck currently has a 6-in pro Comp suspension lift... 2011 tundra..

 

A 2 inch spacer on a 6 inch lift.

 

Would depend on your rear lift, if all the lift is from a block, then no spacer required. If a shackle, add-a-leaf, or a new lifted leaf pack were used, then you will need a spacer.

 

For the 4" block (6" lift) you need to buy an extender to attach the bottom of the air bag to the axle. Firestone discontinue the 4" extender, there is only one store on Ebay still sell it. or fabricate it yourself.