The main things are trailer brakes MUST work or you will have a hard time stopping, and you have to make sure the load is balanced (10% on the tongue). When I first got our boat 11 years ago, the trainer didnt have brakes. The boat+trailer=3800 lbs or so. I could barely stop it with ZJ brakes in good shape. I rebuilt that trailer with a new axle+surge drum brakes and had no trouble stopping it. I towed a 12'x6' U-Haul open trailer with surge brakes (light load, prob 2,000 lbs) and I didn't even feel it back there.
Air bags in the rear coils really help with the tongue weight.
I towed a cargo trailer fully loaded, no brakes (3000 lbs) with my WK and no problem stopping, WK brakes much better when towing.
2007 WK Limited Hemi QDII
1998 ZJ Laredo 4.0 Selectrac