The salt may have been a concern, but I can guarantee you he meant sand. Most LHS think that running on sand is like the anti-christ of RCs. The reasoning that they use is that sand and engines equals a big mess. What they fail to realize is that sand in anything can be a big mess.
Just ask Eddy...sand in his eyes from sleep and he can't read.
Anyway, if you want to run on sand...
You must have a good quality air filter. Make sure that it is securely fastened to the carb. That should keep the sand from entering the engine from that route.
Next, make sure you have a good fuel filter and are very careful to not allow any sand into the fuel tank during refueling. This should keep the sand out of the engine from that point.
Next, select a good set of tires for sand running. The stock tires should do fine, but a good set of paddles for the rear tires and some bow ties or mulchers for the front should be sufficient to the task.
Finally, make sure that you give the truck a good cleaning after you finish running it on the sand (if this is beach sand vice desert sand...the salt thing comes into play and a good cleaning will help keep the corrosion down). It is important to get the sand out from around the moving parts....sand...even loose sand acts like sandpaper when sandwiched between moving parts or a moving part and a stationary one. This would be bad for anything that meets that criteria.
Regardless, running on sand is definitely do-able. Have fun!