I think creaks and groans are normal for a settled build. Mine is a 2006 as well, and while mine has been put through offroading as well as normal use, they should all settle to some extent- this comes loose, that rubs on that. I've found many screws that have backed themselves out and panels that are slightly out of place. My countertops are loose too.
Anyway, you might go through the van and see what's loose and what's shifted and see if that addresses some of the noise. Also note any sounds when getting in and out of the van while camping or stopped- if the noises persist while doing such things (also note creaks and groans away from the van- getting up from your camp chair for example) as it's possible we're all just getting older.