Not really needed to deflate tire - could cause more issues doing so....

when the temperature drops. Statistically, your tire pressure will fall about one degree for every ten degree drop in the temperature. So, with some temperatures varying as much as 50 degrees between summer and winter, you can see the effect the weather has on your tires.

So in winter - do not have to deflate - just don't inflate in mid winter unless really low.

You want to keep your tires on the bead of the rim - deflating them may cause it to be come too low and the rim sitting on the ground and off the bead.  Rust could form on the bead area and allow water inside and rust it as well.

Tips:
- Cover tires (specially if outside)to prevent UV exposure and Ozone cracking Many People use vinyl covers or plywood boards.
- Fully inflate tire to no more than the MAX pressure rating (as listed on tire) on a normal temp day. This is to allow the pressure to drop when it get cool and still be fully inflated. This may be more than is normal in traveling pressure.
- Before you pull the trailer - check ALL air pressure on all tires - including the spare (it will be the ONE time you forgot - will be the one time you need a FULL spare)!
- Rotate your tires - just like on a car. This make sure even wear and prevents RUST on threads from making emergency replacement difficult. Check for excess ware - the most common, if wears too much on the inside on both sides - your axle is bent from overloaded (and/or over time). Most axle are bent slightly up in the middle like / but only a few degrees so when loaded they straighten out.
- Check, from time to time, your tires for cuts, cracks or bulges in the sidewalls and the treads. If they are present, replace that tire because it poses a danger each time you hit the road.
- When you change tires on a rim - have them replace the valve stem. The extra little cost is better than a flat tire a few miles down the road.
- Special Tire dressing/blackeners DO NOT USE! - Tire manufactures do not recommend any type of dressings or cleaners other than soap and water and say that keeping your tires clean is the best thing you can do to minimize ozone damage.
- Care should be taken to avoid prolonged tire contact with petroleum based substances: oils, fuels and asphalt.
- For LONG term storage - Should be raised on blocks, if possible, so weight is removed from the tires.
- If not blocked should be moved every three months to prevent flat spotting and ozone cracking at the tire sidewall flex point.
- Storage area should be level and well drained. Else if you use leveling blocks under your tires the blocks should be large enough so the entire foot print of the tire will fit on them. If you have a dual wheel axle both tires must be completely supported. If you have a multiple axle trailer the tires on the side being raised should be supported equally.

Hope that has helped!