1. All 4 litre v6 frontiers have at least a 6000 lbs tow rating. Not all of them come with the hitch or wiring but adding it only costs about $200 and they are prewired you just have to add the plug, relays, brake controller and bolt on the hitch into the factory holes.
2. Trailers under 3,000 gvwr are unlikely to have brakes but they could be there. Easiest way to check for brakes imo is look at the wheels of the trailer, if it looks like there’s a drum under there they have trailer brakes. Also if you see wiring (for electric brakes) or hydralic lines (for surge brakes) going into that drum you can be sure.
3. 2wd frontiers are actually rated higher in towing than 4wd ones, if you’re not going down any extreme offroad situations then I wouldn’t worry about 4wd. The only time I’ve needed it when towing is when I went up to a friends cabin in the north woods of nh which is several miles of dirty road. It was just a precaution still. With that much tongue weight you probably won’t loose traction.
4. Just the hitch, wiring, relays and brake controller should outfit any frontier. Many will come with some of these things either from the previous owner or from the factory. It seems like you’ll want a mechanic to install these things anyway. They’ll know what you need, and it won’t be very expensive.

 

This is exactly what we needed to know! Awesome and thank you so much!

 

Personally I would want 4x4, we were on a trip into rural/forest areas several years back and a guy was stuck where the dirt road went down into a small valley and back up out again because it rained on him camping and he didn't have the traction to drag his trailer out with his 2wd truck. At the time we were driving a Chevy Tracker with street tires, so we weren't really in a position to help him.

If you were going to tow a small car on a trailer, or even a travel trailer unsuited to really going far from the pavement I might be more comfortable with a 2wd truck, but a popup seems like something one might take further from hard asphalt where one might get into trouble.

 

I would add that muddy hills or boat ramps often call for 4WD as well.

 

You should be fine with 2wd. If you ever plan to tow a boat I would get 4wd just for the ramps. If all you are towing is a popup you do not need it. I would get trailer brakes for a camper that heavy though. Even though it is fairly heavy for a popup it should still two pretty well as it will have much less wind resistance than a hard side camper. If its an option I would get a truck with the factory tow package. You might not need it but it can't hurt.