Leaf springs flat on 2015 Aerolite 294RKSS

I had the same problem on our 2014 FR Cherokee and tires started rubbing the bottom of trailer. I ended up having the whole suspension system replaced last winter, going from 3,500 lb axles to 5,200 lb axles.

The shop I found to do this takes your old parts in on trade to reduce cost. This shop is about 150 miles east of your location. Send me a PM and I'll give you details.

The tempering process can be tricky. It possible to get a bad batch. Too hard and they break, too soft and the flatten.

Sometimes heavier spring pack involve moving the outside purchases, if that is too much bother, have them add a second main.

You need new springs and more of them.

When off warranty and/or fixing axle area problems, I alway +1 "up size" its leaf springs packs. And where possible, upgrade the axle as well. For example, replace factory 3.,000 lbs axle with mew 3,600 lbs axle. And, upgrade with 3,600 lbs leaf spring packs as well.

Remember that many trailer makers subtract 13% off the Trailer's GVW number (assume 13% weight is on the Tow Vehicle's hitch), then divide remaining number by the number of axles. On the "white board", it appears the smaller axle / small leaf spring packs are the correct size. And, save RV maker parts money. Maybe true for some lawyers as well. But IMO (being a certified Engineer), the factory axle and leaf spring packs are "under sized" for the trailer's GVW number. Thus, why I always "up size" without using the 13% Tow Vehicle hitch weight number.

Like I always tell my wife and others... Better to be over engineered / over safe instead of at minimum factory build specs (and risk leaf spring pack breaks across double railway tracks). But, that's a topic for a different post....

Average Shipping Weight (lbs.) 6,748
Dry Hitch Weight (lbs.) 803
Cargo Capacity (lbs.) 852

There's your problem. 852 lbs for CCC. Guessing you've been running over the TT's GVWR the last two years.
Just running with the fresh tank (78 gal) full would use up most of your CCC.

Mine went flat in 2 years replaced with 7000Lbs springs instead of the 5200 and wet bolts from Etrailer.com.

Order a wet bolt kit with bronze bushings when you get new leaf springs. You will be surprised how worn out the plastic garbage they pass off as bushings are.

none in 30 years of towing

Mine were 15 years old. Previous owner upgraded from 3500 lb axles to 4400 lb but kept the original springs. Towing on the bumpy road to mexico one started to flatten and both ends of the second over hanging leaf broke off.

Replaced 1 to get home, once home replaced all with 4400 lb springs to match the axles.

On the scales the TT was at 7000 or slightly above if tanks full +~400 lbs.

Yes. I had flat and broken springs on my current trailer. Even the new ones were too flat. I don't believe the springs sold now meet their rated specs as I was never overweight. Go with a higher load spring to retain the appropriate spring arch. In my case going from 1,750 lbs PR-4B springs on 3500 lbs axles to 2,400 lbs PR-4 springs restored the arch and raised my trailer 2".

Yes and was causing alignment troubles too. I also put on heavier springs and upgraded the suspension. Has never ridden better.