I always blow the lines before filling water lines with antifreeze. Make sure to pour enough antifreeze down the drains to fill "s" traps. Donot forget to run antifreeze thru the toilet ... that little valve while split very easily and is quite expensive.
Remove any food or crumbs from unit. Mice will go after anything. A good cleaning of carpet is also a good idea.
In order to keep the mice out, we have tried just about every posted method. We find Irish Spring soap to work the best. We go to our local Costco and get a big package. Using a sharp knife I shave each bar into slivers in order to maximize serface area. I will then put the equivalent of 1/3 bar into an open zip lock bag. Place one bag into each basement storage compartment and several throughout the unit. I use about 8 on the inside of a 40ft unit. In the spring when you take the unit out of storage ... simply zip up the bags. We normally replace every 2 years.
A good coat of wax on teh exterior of the unit with help with sun fading ... a cover is even better.
Make sure to cover the tires. UV rays will deteriorate the sidewall prematurally.
Close all blinds to prevent fading of furniture fabric