is a surge protector necessary for a basic travel trailer?

Your basic trailer has just one thing that is worth more than $300 and that is the air conditioner. Air conditioners can be damaged by low voltage, so an inexpensive volt meter can tell you when it needs to be turned off. With an expensive EMS everything will be turned off if the voltage drops too low. One thing for sure is that there is a 100% chance that there will be $300 less in your wallet if you buy one and there is a very small chance that it will ever save you more than that.