PUPTENT, according to the stats that you quoted, you will probably be OK with that setup.
With the Elkmont weighing in at 4000 lbs., you are at 57% of the rated towing capacity of the Explorer. Looks like you got some leeway there.
According to a widely used chart used on RV sites concerning towing lengths of conventional trailers, you got a little wiggle room there....but not much. The chart shows the TV wheelbase, and the total trailer length.
110" 20' * 150" 30'
114" 21' * 154" 31'
118" 22' * 158" 32'
122" 23' * 162" 33'
126" 24' * 166" 34'
130" 25' * 170" 35'
134" 26' * 174" 36'
138" 27' * 178" 37'
142" 28' * 182" 38'
146" 29' * 186" 39'
I am pulling a 28.5 footer with a 145 wheelbase truck, which puts me near the limit.......but my combo pulls fine.
The frontal area is probably going to kick your Explorer in the butt with gas mileage. I went from ~15.5 mpg with my 2720 to ~10.5 mpg with a 5500 lb., 28' conventional trailer.
I would think that 7'6" width will help some with the frontal area problem......I have an 8 footer.
You will need a good sway control system. Get a good combination WDH with built in sway control, like the Equalizer (or generics) or the Reese Dual Cam (I got that 1, and it works great). Of course if you can afford it, the Hensley hitch is supposed to work the best of any.
I presume that your Explorer came with a towing package, that would include a class 4 hitch, auxilliary transmission cooler, and a 7 wire trailer harness ??
Since you will be pulling in the mountains, I would highly recommend a transmission temperature monitor. The Aeroforce or ScanGauge II should do the trick......I have the ScanGauge and it works great.
The Elkmont came out about a month after I bought my Surveyor.
If I had only known.