I could be mistaken, but I think you can find info on your vehicles towing capabilities in your owners manual. If not try contacting a Ford dealership and speaking with someone in service. (or if you have a good relationship with the salesperson who sold you your Explorer that may be a route as well.)
As far as "Is one brand better than another?" I asked the same questions on the RV boards when I started my search last year and boy did it spark some flames.

Everybody has their favorite and I have found that no one likes having anything negative said about what they chose. That being said, I think there are lemons in every line and every line has had problems that they have generally worked through. Two big deciding factor that will sell you on a particular brand are the "goodies" and floorplan. They can differ greatly from brand to brand. (I personally don't care for the ones with the table in front of the bed, and looked for a model that had the dinette off to one side.....example of personal preference.)
Once you look at some new units and get an idea on what size and what layout you would prefer, then you can start looking into the used campers that fit that criteria. We made the mistake of doing the "what size and layout do we want" phase by looking at used models. But by the time we saw a variety and made up our minds most of the units we looked at and liked were already sold. A good buy moves quick, at least in our area.
First thing first....open up the camper and take a sniff. A musty moldy smell is a no no. ( one we sniffed smelled way too much like moth balls and upon investigation we found not only mildew, but a urinal cake used to mask the mildew smell) Mildew and campers do not mix!
Some other things to look for {for pop ups in particular}............damp spots in cabinets, in storage spaces, all the nooks and crannies.....mildew, mold or tears on the canvas anywhere....cabinets, or doors that just don't seem to sit strait (possible bent frame)....you have the right to watch them put it up and down, this should go relatively smoothly, otherwise there could be problems with the lift system......try out the lights, gas and water.......
good luck and happy hunting.
- lori