I also wonder about the dealers who insist that no WDH is needed
Furthmore, most vehicle manufacturer's require that a WDH is needed for any trailer weighing more than 5,000lbs. Toyota does and I bet that Chevy does, too.
I think you'll be 5,000 plus on that trailer with a tongue of around 650-700 at least.
(My trailer and yours have nearly the same listed dry weight and mine came out of the factory weighing 330lbs more than the "dry" weight because of my options. When I load it, its weighs in the range of 5300-5400lbs with full propane, two batteries, some water, and our gear and supplies.)
You were right to question them further. Here's the skinny. I will admit that I am not very partial as I have had two Equal-i-zer 4-point on two trailers and I recommend that you stick with that one.
Your understanding of the E2 is dead-on. Economical but can also be good for those set-ups where a less robust system is all you need. Regardless, its not for you. 4-point sway control is worth it.
Besides, the $170 price difference isn't that great. The Equal-i-zer 4-point
can be bought delivered from RVW for $439 and the E2
The Equal-i-zer comes in 400, 600, 1,000, and 1,200lb bars and the 1,000 lb bars are what you want. I'm not sure why they skip 800 but they insist that their bars are flexible enough so they recommend up-sizing on the bars.