The smaller the towed trailer the easier it is to get in and out of places. Think of parking a small car as opposed to driving a bus...same idea.
Smaller trailers don't usually need the hitch stabilizers so you don't have to arm-wrestle them on. Drop the trailer on the hitch receiver, hook up tow chains, attach the wiring and go....well, okay, remove wheel chocks etc.etc....
Not all trailers, even of the same size, tow the same way. It all depends on the manufacturer - how long they build the tongue, how stable the trailer is to begin with, the type of axle, size of tires etc.
If it all possible, take a couple of trailers from different manufacturers out for a test drive before you buy.
I've towed 2 radically different sized Wells Cargo trailers in the past 25 years and I won't tow anything but them....I sometimes forget that the small 6 x 10 I own now is even behind me....well fully loaded with the kids furniture I knew it was back there. Empty..not at all..
It took me six months of diligent searching to find a cargo van with low mileage, new enough and in the right price range so it's not something that unless you're extremely lucky is going to drop in to your lap overnight...have patience and widen your search area.
The high top cargo van will provide enough of a wind stop that the a smallish cargo trailer won't make any difference at all...at least as compared to a 27' travel trailer.
BTW, high tops can be had with full steel roll cage inside...mine does. It has 1/4" x 2" steel frame welded to the original roof at the sides. Any good fiberglass roof will be able to hold all the solar you can put up there. However, one has to think of how one is going to keep the panels clean. JiminDenver had some interesting test results of clean versus dirty panels - the increased power was immense. Because of my desire to keep the panels clean and my inability to climb to the height of my van I chose portable panels....certainly an option especially because you're towing a cargo trailer for extra storage and room.