weight distribution

The trailer's hitch weight and your tow vehicle are the determining factors. Be aware that dry (advertised) hitch weight does not usually include LP bottles or battery. Water weighs 8.3 lbs per gallon; where is the fresh water tank located? Are you planning to tow with a full size pickup, or a small SUV or minivan, or something in between? FWD or RWD? The rear suspension and hitch receiver attachments have to be up to the task. You don't want to take too much weight off the front axle of a FWD vehicle, and you don't want your headlights in the tops of the trees. We need more info.

More than likely the Mini or the Sonic is so light weight, you won't need weight distribution. They are designed to be pulled by the family SUV. The question you need to ask yourself, does your tow vehicle have enough muscle to tow, especially up and down those mountains. More important, does your tow vehicle have enough braking power to stop both tow vehicle and trailer in the event of trailer brake failure.

See my signature line below for the best advise I can give you:

WD hitches can be affordable:

https://www.harborfreight.com/10000-lb-capacity-weight-distributing-hitch-61720.html

I have a 2011 Silverado 5.3, 3.73, and added Air Bags, Bilstien shocks, and E tires, My TT is a tandem axle GVWR of 5,300 (actual is -4,800) TW 530. No WDH or sway bars.

Airbags help in leveling, but I get a little sway, not white knuckle.

IMO you should be okay.

A WDH may or may not be needed depending on your tow vehicle's rating, your hitch's ratings, and your trailer tongue weight. It has everything to do with weights.
It has absolutely nothing to do with going up or down a mountain, rain, or being passed by large trucks.

As mentioned, only with accurate weights and ratings should anyone attempt to tell you what you need or don't need. I happen to choose more than adequate tow vehicles in order to eliminate the need for any WD hitches. Call me lazy, but "Drop the ball on the hitch and go" is my preference.

Our short list before buying a new trailer (2 weeks ago) were R-Pod, Airstream, Winnebago Micro Minnie and a Sonic. We finally settled on the Airstream, but we WOULD have used a WDH on any of the 4. Going up, or worse, down, a steep mountain grade in rain and high winds with semis blowing past is a nightmare of mine.

This depends entirely on info we dont have, like what tow vehicle you have and what the weight on the tongue is.
Also, don't believe sales people. They are the most ignorant people on earth when it comes to technical RV matters.