I have been having my cars Rust-Checked [don't know if you have this in USA] but I would expect something similar
http://www.rustcheck.com/about.asp . My local guy not only does the underside and the motor bay - but does a mist over the entire car just before I put it into storage. I store it in a large barn - gravel floor - unheated. I check all the fluids prior to storage and then pull the live battery cable off. I put in "essence of peppermint" on cotton balls - then fleecy dryer sheets in the motor bay - interior and trunk. This year I will put moth balls around the tires. Last year I missed a granola bar and even with all this protection the critters got in to eat the granola bar. Obviously this year needs a better cleaing prior to storage. The debate as to parking on gravel or having a plastic sheet under the car remains - but my mechanic says no problem in a dry
building on gravel as I am doing the Rust Check. Regards Peter Thielman - 1971 Imperial LeBaron - 1970 Dodge Polara convertible.