Are you driving alone? Stopping to rest by the side of the road is not a great idea. Especially since the plates on your car will read North American. You are creating a potentially dangerous situation. Bandits roam freely and are quite litterally part of local governments.
Border crossings will result in searching you and your car, and reviewing citizenship.
I would make sure you have contact with someone at home a couple times of week.
Advising your whereabouts. Central American countries are infamous for people gone missing. Especially if you apear clueless and not to belong. Don't talk to strangers should be taken seriously. If this is an adventure you've had your heart set on.... Plan with great detail. Make accomodations prior to leaving the U.S. into Mexico. Give a call number to hotel if you do not arrive on time. Ask hotel attendents for guidance in site seeing.
Not trying to freak you out...... Just true. Intense spanish lesson prior to leaving would be a good idea.
Sounds like a great adventure, but needs to be done with appropriate planning.
Let me know if I can help.
Blessings & Light
Tami
P.S. I was a travel agent for 12 years prior to 9/11. also have central american friends.....