A friend of ours lived in Belize for a couple years. Bought a place there etc. He hung around this Belize forum for awhile. Here is the link. You might be able to get your security questions answered there. Driving there is no problem. Good Mexican interstates all the way and some incredible sceenery.
http://www.expatexchange.com/belize/liveinbelize.htmlNot sure why he left but he sold out there and moved to Chetumal. I know they travelled to Mexico for a lot of their medical as well as major purchases like appliances etc when they were in Belize. We did a quick tour and it wasn't to our liking but some like it. The standard of living is very low there and that causes some problems security wise. The average income is about 1/4 of what it is in Mexico. If you are just looking for a nice low key place to live in that part of the world I would consider the city of Chetumal on the Mexican side. Easy going without crazy amounts of tourism. Right on the golf. Nice middle class city. Here are a few shots of a nice RV park on the golf we stayed in. Its one of the places we thought we would enjoy long term if that ever comes up. Here is a link to their resort.
http://www.yaxharesort.com/ Angela looking very touristy.
Boat launch.
Pool area.
A few cottages if you have friends visit.
There is a restaurant and bar right on site.
Good luck and happy trails.