WEAPONS
The rules vary by state and sometimes by county or city or even by location in a city. For instance, in Tucson, you can be driving along perfectly legally and then suddenly be illegal (get within a certain distance of a school). Parks and campgrounds can add additional restrictions. Since you can practially be guaranteed to break some law at some point in time, your best bet is to not get caught (don't tell anyone and keep them or indications of them out of sight) and appear as harmless as practical if you should get caught. It should be fairly safe most places (except perhaps in New York, D.C. and other NorthEast areas) to have them unloaded and locked separately from any ammunition, in an area inaccessable from the inside of the transporting vehicle and in a difficult to remove container.
Of course, this would be worse than useless for defensive purposes. A compromise would be to have one unloaded, with loaded speedloaders/clips, in a locked box bolted/chained inside the RV. Key locking would probably be best (for access without vision) , although they make a vault with a touch combo lock which could be a good choice. Another choice would be to have a remote, hidden, unlocking switch.
I have heard of a 'passing through' federal law which claims that if you are travelling from a place where you are legal to a place where you are legal (and meet minimum transport requirements, I'm sure), you 'cannot' be charged with possession in places between. Nice, but no guarantee of a hassle free trip, and for every law, there are infinite exceptions and interpretations.
If you are crossing into Mexico, do NOT have ANY firearm or even ammunition, unless you are desparate for new and exciting experiances (and have large amounts of disposable resources). If you are crossing into Canada, contact both the Canadian (and US, to get back in) governments and find out the current restrictions.
Check into getting a licence for the place you spend the most time; some places offer reciprocity of licences, and even if the license is no good where you are caught, it may help by showing you have had a background check and some training.
For more specific info, see
http://www.recguns.com/Sources/OutII.html and the following books:
Gun Laws of America: Every Federal Gun Law on the Books: With Plain English Summaries (3rd Edition)
The (states of interest) Gun Owner's Guide: (authored by Alan Korwin, there are only 5 states listed)
I've seen a booklet listing laws of all states, but I can't find any source today. Check with gun stores, gun shows and ads in gun publication.
