What is the tow rating overseas? I bet it's high enough "over there". But "over there" towing speeds are lower, and they run lower tongue weight. Both work hand in hand to lead to sketchiness, but technically it can be done.
5 trips a year? Every other month? What kind of miles are driving outside of that? I feel like this is on the edge of "just buy a bigger/better vehicle and eat the mpg the rest of the time". Something with 3,500lb towing.
Now if this is something you already own, well I'd try at least once. Leave it out of overdrive, and drop it into 2nd on hills. High rpm isn't evil. It's good for the trans if anything, keeps the TC in a low slippage region. If you don't have a trans cooler then I'd definitely add one though. I'm going to guess the rear is going to squat with any amount of weight, so airbags would probably be a second mod. The I4's had a different trans than the V6's, and they all had different coil springs in the suspension--but "frame" etc are all the same, and the V6 was rated to 3,500. I think they all had the same brakes... which is the third point. If you were doing just 1 ATV, you would probably be fine without trailer brakes. IIRC the manual says to use trailer brakes above 1,500lb across Toyota's manuals (might 1,000lb). But with all these miles you probably should be looking at trailer brakes.
As always, speed is your friend. Err, lack thereof I should say.