Your Airstream has nearly 14,000 days & nights history... Don't read further if you just want a quickee camper. Okay, pull off the kid gloves...
I had mouse dung dunes in the duct work. The uric acid from the incontinent little squirts had grown sculptures of oxidation in the sheet metal. Banishment from the interior was the only recourse, to be acid washed and allowed to weather under the stars for a few months.
Get on roof and check the plumbing vent tube(s) extend above the vent stack gasket, oh; and that the vent gasket is still there. The black plastic pipe is held up by obliquely placed band clamps that did not hold mine up, somewhen that first Dukes of Hazard hop let it settle down and left the tank venting inside (eww) well offset from the shell port and without fail somewho never caught on, bless their little pointy head.
My '73 had spilled formaldehyde black tank chemical in the galley shelves, and seepage from rotten commode mounts. The formic acid byproducts of the old style tank chemicals are nasty, we washed every available interior surface and it still stung eyes and throat.
Pull the bathroom panels and you'll be amazed when you take out panels the amount of gunk living on the hidden areas.
Pull the carpets. Paint bare floor to smother smells, leave a gap around the interior liners to spot water seeps and allow it to dry. Everyone like the smell of paint, right?
Its been two years and my trailer still isn't done - there are some nice posts about what I have done, I invite you to read them, there is more odor control stuff scattered about in them and I now disgusted myself again so I'm out for now....