i did have this type of problem on a 2001 278EFS Cougar (also a keystone product)
i had a problem with the leaf springs breaking. the camper wasnt overloaded, but it broke the rear, pasenger side leaf spring two times. i finally replaced the spring with one from a different company and never had any more troubles. also one of the shackles had the hole the bolt goes through wear so bad that the hole almost broke through the end of the shackle.
for replacement springs, shackles, and bolts, i went through Redneck Trailer Supplies.
after replacing the worn and broken parts with Redneck parts i had no more problems.
Keystone wasnt much help on this issue. the first spring they paid for the repair at another dealer. the second spring was out of warranty by 4 months and they never even replied to my calls and letters.
since that experiance i always keep an eye on the suspension.
here is a link to Redneck if you need it.
http://www.redneck-trailer.com/
hope this will help
Merv