Fair enough...
Start with spending some time with these videos, of course it's published for the United Kingdom, (metric and right hand drive), but most of the basics apply. We don't have handbrakes on the trailers, and our driver's licenses don't have trailer weight classifications (generally).
This was my brake controller, very basic, it sends power to the electric brakes on the trailer at a rate set by the adjustment wheel on the controller, when you push the brakes on the tow vehicle. There are much fancier controllers, I just wanted the basic one.
Reese Pod brake controller
In my prior post, the picture of my factory receiver hitch shows class III max 5,000 LBS towing, with a 500 LB max tongue weight, and not rated for a weight distributing hitch, so find out what your hitch is spec'd for. You'll also see I chose an extended ball hitch to clear the rear door/tire.
My '02 limited has a GVWR (Gross Vehicle Weight Rating) of 5,840 lbs. (look at your driver's door sticker). That means that the truck, when full of fuel, you, wife, wife's dog, (neighbor's dog), tools, luggage, cooler, gear, etc. has to weigh less than 5,840
with the trailer connected to it. The tongue weight, is the portion of the weight of the trailer applied to the ball. So just for fun, 5,840 - curb weight of empty Montero (~ 4,600) leaves you 1,240 LB cargo capacity, minus fuel, folks, stuff, and tongue weight. It adds up quick, but if you are careful, it's doable.
In your popup example, a 4,300 LB
loaded trailer, the tongue weight is typically 10-12% of the loaded trailer weight, so you could already be above the maximum tongue weight of your hitch for example, even though you are still under the 5,000 LB max rating. 4,300 * 12% is 516 LBS! (Oops). Good news is, I imagine a typical popup might not have a 12% tongue weight, but you won't know for sure until you drive across the CAT weight scales.
Don't despair, just take your time, and think this stuff through. Don't just hookup and go. The camper salesperson likely will tell you whatever you want to hear, so be realistic. Also don't get too excited and get too big of a trailer, or your Montero towing experience won't be much fun at all.