This is a fairly common question to be discussed on the various RV forums. Unfortunately, most times when it comes up it soon gets very heated since there are many different reasons for owning guns and very strong feelings about each. Some of the reasons for wanting to carry a gun are for sporting purposes, for personal safety and for heirloom value. If you are a fulltimer and have no other home it is often a problem to find a place to safely keep firearms that may have sentimental or antique value, as well as the fact that most guns of any quality have become quite expensive. So if you own a gun, there is a good chance that you will want to keep it in your RV, at least on some occasions.
The reason a person carries a gun plays a major part in where they will probably wish to store them. The carriage of long guns when they are not loaded, and kept in a locked case is usually not a legal problem. If they are then locked in a compartment, not accessible from the passenger area of the vehicle when traveling, there are only a few states and cities where they would violate any local laws. But there are places such as Washington DC that there is no legal way to pass through with a firearm. Guns kept for personal protection would usually be kept in an easily accessible location, at least for occupants when stopped for the night. An empty gun that is locked away and far from it's ammunition is not of much help for security. The better the access to your gun, the more likely that you will be violating local laws.
If you happen to be a person who does not own, or desire to own a gun, the issue is very simple. Don't start. There is no easy answer to this for people who wish to keep a gun. The best way for gun owners to deal with legal issues is to first be well informed about the laws in the areas you plan to visit, or pass through. The best book that I have found, by far is "Traveler's Guide to the Firearm Laws of the Fifty States." It was written by J. Scott Kappas, an attorney from Kentucky who is both a practicing attorney and the owner of a gun store. It can be easily found on the internet. If you are considering this choice, the book is very inexpensive and easy to understand. Good choices start with understanding what is at risk.
My personal opinion is that for anyone who is not already experienced with firearms, this is a very foolish action. Guns require constant practice to be helpful in an emergency, particularly if you choose to buy a hand gun. It is also important to remember that the value of a gun for safety only comes when the owner is willing to kill someone with it. It is very risky to show a weapon if you are not willing to use it, and if you plan to use it, you should plan to kill someone. The idea of just winging the offender is one from movies and is totally impractical in an emergency. Those who have experience with weapons, such as retired police officers and similar professionals are qualified for this. Many others who have extensive experience could use a gun safely and gain security from it, but to buy your first gun just to carry for protection in your RV is not a wise idea, in my view.
If you feel the need to own a gun for safety reasons, the very best choice of weapon is a shotgun. There are several reasons. A shotgun requires very little practice to remain proficient with at close range, which self protection will be. Shotgun pellets will not pass through a neighboring RV and harm an occupant, while large bore handgun bullets would. There is nothing more threatening to an intruder than the business end of a shotgun. The noise that it makes, should you fire it will frighten most people into making a very hasty retreat. After many years of experience with guns, I believe that a small, 410 or 20 ga. shotgun, loaded with #4 or larger buckshot is the most effective weapon in the hands of most people. As with any gun you need to practice frequently.
Give this question serious thought well before the time should arise and choose carefully. In more than thirty years of RV travels, I remember only two times that I ever felt any need of a gun for security. Looking back, the wise choice then would have been to have left the area, but I was much younger and more inclined to stand my ground. In neither case did anything happen, so the history would be the same even if I had not been armed, which I usually was back when we lived in Wyoming. I believe the best course of action today is to make your own choice, based upon your experience, and after learning about the legal issues that could arise in the event that you choose to travel with a gun. Once you make that choice, do whatever your choice is, quietly. There is no reason for anyone to know if you keep a weapon or not. You are least likely to have a problem in traveling with a gun, if no one outside knows that you have it. And should you come into contact with law enforcement authorities, decline if the officer should request to search your RV. In most cases there will be no negative effect from such a denial. Use good judgment about where you will keep a gun, to prevent any child or inexperienced adult from harm.And understand exactly what it's use means and what you will do with it, before the day comes to make that choice.
The best way to be secure in your RV, with or without a weapon is in your choice of where to stay. If you spend nights in parking lots as you travel, always pick those which are well lighted and where there are other travelers around. Consider the look and feel of the community and don't stay in a bad part of town. If something should make you uncomfortable, pack up and leave. Better to move on needlessly than to have a sleepless night, fearing trouble. Even if I happen to have a gun in my RV, I would never spend a night in a location where I thought there was significant chance that I would ever have to use it. In more than nine years of RV life there has not been one occasion when I would have even thought about a need for a gun. Even when in remote areas, it would be very unusual to need a gun, even for a wild animal.
Another thing to keep in mind about carrying of guns is that Mexico forbids the crossing of their borders with any form of firearm or ammunition, of any kind. They are very hard on those who they catch violating their laws on weapons. For Canada, no pistols of any kind are permitted and for long guns you need to get permits for them before you go. I suggest that you contact Canadian customs well before you plan to travel there and make sure that you know the current regulations on this issue. It seems to us that Canadians believe that nearly all Americans carry a gun so searches of RVs is quite common.
We do just as I advise. Since I do own guns and always have, I read abut the laws and keep a current copy of the suggested book. As to what I carry with me at any given time, only Pam & I know for sure.