Hi, jaimez. I'm a fan of small trailers and have owned several. The first thing you need to watch out for is hitch weight. Your van probably is rated for about 350 lbs on the hitch. Any more than the rated weight will adversely affect the rear suspension, take too much weight off the front tires for traction and stopping, and could even tear the hitch receiver off the van during travel. That Salem has a dry hitch weight of 385 lbs. Too much! And 'dry' means without propane, maybe without battery, and definitely without any water or cargo in the trailer; in other words, real-world hitch weight will be more, sometimes WAY more, than the dry weight. Best strategy is to find something with no more than 275 lbs dry hitch weight. And you need at least 10% of total trailer weight on the hitch for good towing characteristics (no sway), btw.
Second: the biggest drain on your drive train will be wind resistance. Total weight will bite you more on the hills (the steeper the hill the bigger the bite), but towing a trailer with lots of frontal area will be tough on the minivan. One solution is to plan on driving more slowly, like 55 or maybe 60 mph. But you're still best off to look for a trailer with the least frontal area possible that still has the space and features you think you need. The Salem is taller and wider than the R Pod, thus it would tow harder.
A 16' Scamp will cost even more than the R Pod, but it will tow easier than the Pod because of its small frontal area and light weight. Layout #4 has bunks up front and dinette in rear that makes into a bed (the old ones have a very narrow "double", about 48" IIRC, but new ones can be ordered with 54" width). Hitch weight is likely to be under 300 lbs, and total weight around 2500-2700 lbs, when loaded.
If you don't mind 'basic' and 'no frills', you might be able to configure one of these
Eureka Rambler 6.5x14 trailers to suit your family's needs. They are pretty affordable and I think they will customize the interior layout.
Of course, there is always the tried-and-true popup trailer, with canvas sides and pull-out bunks. These tow easily down the highway since they fold down so low and tuck behind your van. A hard-side option in folding trailers is the
Aliner. Even their largest, heaviest Expedition model would work with a minivan.