the upstairs is better supported on the 2004 than the 2002. ie it should give less.
tires are important. the tire can damage the side and under a trailer if allowed to run till it comes apart (i did that because i didn't know i had a flat).
i can't think of anything else to tell u to watch for. the cracks are the only major thing to go wrong on mine and they didn't show up till this year. with that, i will say, enjoy it.
if u don't have cracks yet, i would suggest going ahead and putting the cross brace in. there is a suggest frame repair on lippert's web site.
MOR/ryde Trailer Crossmembers - PPL Motor Homes
has an adjustable one.
the picture is the way the factory recommends it. one would go between each spring support.
(the picture below was borrowed w/o permission from another club member)