Parking outside after washing? Way better outcome than leaving the salt on it. Really, about the only issue will be the doors and windows icing shut. This obviously in very undesireable next am trying to get to work on time. Some chance that you will damage the rubber weatherstripping too - by pulling hard on a frozen door. Some damage you'll damage a door handle by pulling too hard. All 3 issues can be managed.
In desperate moments with a stuck door, you can douse your door frame with warm water (not boiling or you may actually burst your window) - or if you have remote start, and have left the heater on - start and let it run a few minutes and try the door again. Eventually it will thaw. And if you need more than one door open (wife?) - get one open and then push open others from the inside. Way easier than pulling like a demon on the door handle from outside.
And you can do a couple of things to prevent serious freezing.
- Spray down your rubber door seals with a silicone spray. Inside window channels too. Do this when it's warm or do it in a warm garage. Needs to dry a bit.
- Take a couple of cloths or old towels with you to the car wash. After washing and before going out into -20, take a couple minutes and open all your doors and wipe down all the rubber seals where they meet the door frame. I wipe twice, second cloth gets things pretty dry. This dramatically reduces amount of water that can freeze, and although your doors may stick a little in extreme temps - I've never had a door freeze solid and not open with minimal drama. This may mean using wand wash, as you may not have time or place to do this when using drive through wash.
- if weather is just ridiculous cold (-30 kinda thing), and you're ok with this for security reasons...leave one door "on the latch". As in, not fully closed - just to the first latch. You should still be able to lock the door - but maybe have to use the key in the lock. Remote lock will probably not work on a partly closed door. You'll still get a partial seal on the door, so snow getting inside truck will be minimal or none. Of course this opens possibility that your door lock will be frozen and unuseable. For door locks I use a product from Amsoil - MP - a very light lubricating oil that leaves very minimal residue. Is used on guns and other delicates. Been using it in all my keylocks including ignition for years. Maybe silicone as second choice. Would hesitate to use WD40 or other sprays for this.
And don't try your power windows until the cab is nice and toasty. And then try real careful with a short burst on the button. If it sticks, leave it alone for awhile. You can cause metal to bend or plastic parts to break down in the window mechanism by trying to hard to open. The motor is stronger than the other parts down there in most cases. If you absolutely need to see what's out there - open your door and stick your head out thata way. Another reason to have a backup camera - which only works when your vehicle is clean by the way.
I live in Alberta - park outside - and wash my truck a lot.
As to using hand wash compared to automatic with underbody spray, I have no experience with the later. I guess try the automatic (you've already bought the pass) - but maybe take a real close look one day after it drys, after a salty day. Look real careful underneath and up in the fenderwells. You should see dry salt if it's been missed. That'll tell you to use hand wash, or maybe both? I find it hard to believe that any automatic can be as thorough up inside wheel wells and also engine compartment, but probably better for underside where it's hard to reach with a wand. Seems like the automatic wont' do engine compartment at all except for underneath. I'd probably do both once in awhile, especially after a drive where your car is really covered.