The problem is those stupid propane tanks up front. They were on the jayco as well. Unsure how the popup camper originally towed when it was new. I obtained it as a flat trailer and went from there but the front hitch point of the trailer is beefy. Seems like they should have put a heavier duty axle on it as well. Go figure.
...stripping it down to just the stuff you NEED vs the stuff you might need is essential in every trip,...like taking one empty tank of propane, and getting it filled or traded for a full one when you get to your destination.
you could HOPEFULLY move some stuff off the front of the trailer, and put it on the rear or at least behind the axle,
oh and on axles there always seems to be options for better stronger axles on all trailers, but it is up to the buyer to actually tell the builder to use the stronger ones.
you might do some more local test runs around with the trailer and see how the car performs, like if the water temp goes up too much. A lot can be helped by picking the right time of day, and purposely keeping your speed down. 1800lbs is a whole lot for a 12 year old car to take. (brakes, radiator hoses, etc. etc. etc.)
here is a good long recent thread that talks all about towing, just extrapolate the weights for your car vs. the 2005 3.0, and in the end Chametzoo got a used Jeep Grand Cherokee as he intended to camp off road.
New 3.0 2005 Outback owner... Towing concern!