we store the Safari uncovered and where it gets mostly sun, with windows & vents cracked open when long term weather permits. the Safari is clean & dry inside & out, and we inspect for leaks regularly.
the air inside sometimes gets "stale", though not with the sort of scent that would be cleanliness, or bathroom / sanitation, or small critters related. (I actually think it may be the remnants of the scent from the dryer sheets the PO used to keep the unused trailer "fresh".)
we've used air fresheners, essential oils, and a few other products with mixed results.
Gabrielle found this product in Bed, Bath & Beyond the other day ($9.95, I think?) and it seems to do a pretty good job! Bad Air SpongeŽ - Bed Bath & Beyond
and Bad Air Sponge
thought this might be useful for some.... ymmv.