My 2 bits, go for diesel, look for a pre mid 2007 Dodge. Why? I am a chevy guy, but since they do not sell diesel pickups in Mexico, finding a mechanic who can work on a Dmax or Powerstroke is difficult, any of them can handle a Cummins. If a lter diesel you need to look at Ted Whites infomation at
http://www.mexicorvforums.com/diesel.phpBTW DEF fuid is not available at Autozones in Mexico.
As for a truck & camper you run into a grey area with permits. They do not know if it is a truck carrying cargo or an RV. You can get away with regiterign it as an RV by getting the permit on-line, but that is not a good idea if you intend to take it off and drive around with just the truck. As soon as you add a motorcycle ot the permit, the 10 year will become a 180 day. now comes the issue of the bike, It it is over 150 cc, it will require a separate permit. That brings up a problem as you are only allowed one. However, you are allowed one RV & one non RV, so in that case you really do need to do it online and call the truck & camper a single RV. Its a good idea to rmeove the jacks if you od that and store them in the truck bed if there is room so it does to appear removable.
If you do buy that dodge, make sure you carry spare, oil, fuel & air filters for it. They are pretty specific for dodges and you probably will not find them down here. Also the recommended oil is tough to find. Mine was real dirty and I tried to find replacement oil. I got close, but not what they tell you to use. It only has to be in there for 1500 more miles, so I will change it again when I cross into the US. For what it's worth a mechanic told me to use a product called Hot shots stiction eliminater
http://www.hotshotsecret.com/ to prevent injector issues. I have been using Optilube XPD diesel treatment in my truck. A bunch of research shows it has the best rating (I was using stanadyne). It's really improves mileage, I am averaging 17 MPH towing a 25 foot 7000 lb trailer. The weak points with the dodge are the front end & the tranny. Dodge tranmisisons are usually only good for about 125k miles, so if it has not been done you may want to have it looked out. There is an external band adjustment that is the tip off. If there is no adjustment left, then it's due. When they took mine aout ($183,000 kms which is 125 miles)it was down to the glue, I would not have gone 100 miles before trouble. The other issue with Dodges is the so called death wobble. It appears mainly on trucks with lift kits. Anyone comeing from GM or Ford will noticee that Dodges have an uncomfortable wandering feeling. You can do some improvements with products like BD diesels steering brace (about $300 installed). Anotergh good thing to do is to install a FASS or Airdog lift pump. Leave the origina fuel filter in place and these add 2 mor elevels of fuel filtration. A bit pricier with dodges as the internal fuel tank pump has to be removed. You can ge tbad diesel in Mexico as diesel vehicles are not common except trucks or buses. You risk getting stale diesel. That is why you should always try to re-fuel where you see lots of trucks filling up, not in small towns off the beaten track.