I'll be the pro-use/devils advocate. Living in Orange County, driving to fresh water and being back by 10am is an impossibility. So, I have no choice but the ocean/salt water.
After 25yrs. of salt use, we sold our Mastercraft on the original "I" beam trailer (painted). My neighbor who bought the boat replaced the trailer. You would have to tear the block apart to see any evidence of salt use. I figure the cost of use was a 25 yr. old trailer and 1 extra set of manifolds and 15 more minutes spent rinsing it down and flushing it out. We never would have put 1,000 hours on it if we kept it out of salt water.
At the hotel, I would not leave my gear/keys in the boat overnight, even though the dock will be semi-secure.
Prior to your trip, launch your boat at home and wax your trailer. Prior to launching in SD, I would use T-9 spray (or comparable) on the engine/electronics & brakes on the trailer. Check underneath your trailer. It probably has holes that will fit a garden hose. After launching, wash the trailer & brakes and flush inside the trailer tube holes. If you have an I beam trailer, even better. Bring a garden hose as they probably don't have one at the launch. Run the engine when you pull it out for 5-7 minutes (water should get warm/hot). If you run your bilge, fill it with fresh water and re-run your bilge.
If you planning on selling your boat anytime soon, then you may need to consider the perceived steeper "salt water" depreciation curve. I have 2 neighbors with brand new X-30s who won't go in salt. They will use them 3x a year on various 3 day trips. That to me doesn't make sense or cents. Upside is I'm making decent slalom skiers out of their wake board kids :)
When you get home, wash & wax the trailer again and you will have a brand new Prostar that hopefully has 20 more engine hours of great family story's.