Just an added suggestion.....
I tow a lot of pretty heavy boat trailers. Incorrect tongue weight can have some pretty drastic affects on handling, especially on the highway. Before anyone starts experimenting with tongue weight I would really encourage them to figure out a baseline tongue weight with a known handling characteristic. If you know it sways, and under certain circumstances, then set it back up about the way you had it that last time, and then determine that tongue weight. That way you have an idea of what adding 50 pounds (or 100 pounds) will get you. Ideally you don't want to set tongue weight significantly heavier than necessary (and that's a moving target for every trailer), and you want to be able to repeat that value every time you have a long trip planned. Plenty of specific scales out there for tongue weight. Also plenty of cheaper google solutions if you search for "measuring trailer tongue weight using a bathroom scale" (or something close to that). I know that Curt Manufacturing and other towing specific companies have blogs and web pages about the process (and it's quite simple and requires nothing more than a basic bathroom scale (ie, does not need to read as high as the expected tongue weight....don't need a 500lb scale), that should show up in a search. Should be able to find this through some reputable and trustworthy companies webpages.
Also will let you determine how to best deal with water and cargo loads before trips, and how to temporarily fix/improve (as suggested, add weight to the front box), or more permanently fix/improve (as suggested bikes in front, or if more drastic, maybe relocate the spare tire from behind camper, to up in front of the box?)
Anyway, knowing your desired tongue weight (and being able to check it and repeat it on your trailer) will usually allow you some less stressful drives, especially when going by semis in the dark of windy nights.
Huge fan of the bags of sand suggestion when you unexpectedly find yourself on a trip with sway issues. Cheap, easy to find even at night and on weekends, and easy to dispose of in an environmentally friendly manner. Win, win, win!