I am in a similar situation as you. Airbags helped a lot with the sag and handling.
The ride without a trailer is like 15% rougher even with minimum psi.
Unlike some I could not get the bags installed by sliding them into the spring. Had to get them installed professionally.
Curious to hear more on your experience towing this type of load as I am in a similar situation as far as weight goes with a 22 pontoon.
Its actually not that bad. I could distribute the weight better by moving the axles 8-10" further on the trailer frame. But I don't tow this far enough to justify that hassle. I keep the boat in a slip, so I really only have to tow this 2-4 times a year, but never further than 10 miles. I dropped it down to S4 and it towed it just fine, stop and go through town up to 50mph. Based on what I have experienced so far I am not going to do airbags right now.
And just because I like to show off the truck/boat combo...

