If you don't own a truck, a small trailer is the best money you'll ever spend.
Light weight is crucial.
Good handling is crucial, more crucial the lighter the tow vehicle.
Put synthetic fluid in the trans and a good cooler, after or instead of the radiator cooler.
Actually all modern cars need a separate cooler.
Install beefier anti-sway bars.
Lots of shock, spring and bar options for anything german.
Check out trailex if you can afford them.
My trailer is custom made from an early subaru rear end.
So far I haven't seen a better base, but narrow.
Mine is 32" x 8' 5".
Narrow is more aerodynamic and tracks better.
13" trailer tires are available for more weight than you will ever carry.
I also have a long tongue for stability.
You should always try to put the weight in the car and the bulk in the trailer.
Not always possible, I know.
A great approach is a single wheel trailer.
These approximate all the expensive devices used on trailers to control them, but for cheap.
They attach on two points, hinged, and use a swivel wheel.
Normally height is set by the wheel, but I've seen one with an outboard wheel and suspension,
Not sure how that type reverses.
Single wheels drive like one single vehicle.
Surge brakes are another option.
In mountains a full brake set is a good idea though.
Put conspicuity striping all around your trailer.
If you don't like zebra stripe, it is made in solid white and red, many sizes.
I suggest turn signals on the side, besides other lighting.
Side turn signals on your car are a good idea with a trailer too.
Ron Francis has a good, if directional type.
Superior to the euro turn signals.
I like strong reversing lights too.
I can recommend some.
Most are really unsuitable for the job.
I prefer a two inch receiver.
Usually you have to modify or custom make one.
Newer hitches are declining in quality.
All except one brand are chinese crap now.
If you can find an older or euro hitch, get it.
Probably a factory hitch for that car.
I had a 2" receiver on the Sable I took out two years ago.
It's very easy to make a superior hitch to most sold now.
We used a northern tools receiver tube.
I took one look at the crap harbor freight was selling and ran to northern.
I usually adapt older receivers though.