It's safe to use, but there are caveats. Just be aware that a 30 amp pedestal, or other power source, will not run all of your 50 amp load at the same time. You won't, for example, be able to run the hair dryer, microwave, air conditioner etc... at the same time. Also, be aware that the longer the distance, the more "voltage drop" you'll experience. I personally wouldn't go over 25 feet, and I'd keep my load to a minimum. You'll want to run your 'fridge', and water heater on propane to reduce your electrical load to protect circuit boards from "brown out" damage.
This will work for that occasional need, as long as you can accept the downside. I also suggest a quality volt meter to make sure you're supplying at least 110v to the camper.
Another trick for those occasions, is to run a second Heavy Duty 15 or 20 amp rated outdoor extension cord from the pedestal to the camper. This can be used to give you a little extra juice for plug in style appliances. If you sneak it in thru a slider, make sure not to pinch it.
Steve & Jan, Ava & Emma (Mini Schnauzers):
2016 F350 Lariat 4X4 Powerstroke CC/SB "PULLTOY V"
2013 Alpine 3535RE "MAGIC CARPET IV"
Proud Navy Vet!