Rather than trying to get a survey response that would have a valid sample size, I would proffer that the most common trailer found in use for a 190 MONTAUK would be the model that is available at time of purchase from Boston Whaler.
In the specifications, the number of axles on the trailer is not called out, but there is an illustration that shows the trailer is a tandem axle model.

- Fig. 1. Illustration on Boston Whaler website showing optional trailer for 190 MONTAUK. Photo courtesy of Boston Whaler.
- 190mtk-trailer-option_detail.jpeg (36.9 KiB) Viewed 1128 times
On that basis, to me the prudent choice is to get the tandem-axle trailer, even though it will cost more, will weight more, and will be somewhat harder to maneuver than if you got a single-axle trailer with a capacity rating that was just enough for your particular boat.
The listed dry hull weight for a 2026 190 MONTAUK with engine is about 2,800-lbs. One problem you have right now is you really do not know how much your particular boat will weigh when it is on a trailer. Boats on a trailer always weigh more than their catalog weights because they have fuel and a lot of gear aboard, such as batteries, anchors, tools, and other relatively heavy stuff.
Regarding trailer capacity, if you get a trailer that has a much higher capacity than your anticipated actual total boat weight, the trailer springs will probably be quite stiff and the ride quality of the trailer with a much-lower-than-capacity load might be somewhat harsh.
Also, I believe that the optional Boston Whaler factory trailer might be a KARAVAN. You could contact Boston Whaler for details about the trailer, and perhaps even purchase one through a Boston Whaler dealer. Or, if you get the model information, you could buy it from a Karavan dealer perhaps with less markup.
ASIDE: on the 2026 BUILD YOUR BOAT page for the 190 MONTAUK, the trailer is not an optional cost item. It seems that the cost of the trailer is baked-into the MSRP price. Because of that, to know the cost basis for the trailer is rather difficult.