I'm going to place a vote against an off-road trailer as a possible solution. I like trailers, but the main problem with an off-road trailer is simply going in reverse when you find that you cannot continue to go forwards. I've been pulling trailers for many years - did it as a job for awhile, as a matter of fact - and hardly a trip goes by where I find myself in comparatively mild off-road terrain, realizing that there would be no easy way to extract myself with a trailer should I need to simply back down the road that I just traveled. Trailers are fine for those that are simply pulling up to camp by way of the highway or improved roads because the trailer is never going to be pulled anywhere that would get you in trouble (which also sort of negates the "off-road" thing, but whatever)...but if you're camping further afield, I say to keep it all in one vehicle.
As far as the netting idea goes...
If I was doing a drape-over netting, I would find some heavy-duty screening - like the stuff they use on campers and boats - and I would have someone sew up a Jeep cover that's made from screening and that fits the exact same way as a conventional cover, using the same attachments and tension points. In fact, finding a cheap Jeep cover to use as a pattern would probably save you money in the long run, because the person doing the sewing wouldn't have to do all of the laborious patterning and fitting and testing, which is what costs so much when you have custom canvas/material sewn up: you would already know that it would fit when it was done, so they could just go right to work. I would sew a nice reinforced seam along the bottom edge, and I would pocket in some decently-strong magnets to help keep the seam tight against the body of the Jeep, as you suggested; either that, or I would look into some additional tension/adjustment straps that will help you pull it as tight to the body as is possible to keep out the really small bugs. I think it could work; that said...
The most elegant solution would be something that actually clips into your door/tub surrounds and that allows you to keep your doors in place for easy entry. It will essentially fit like a frameless top, but it's gonna cost you: you'll need said frameless top to salvage parts from, and you'll have to find someone that's good with canvas in order to make the necessary seams. Expect it to cost several hundred dollars plus whatever you spend on the top for the pattern, unless someone owes you a serious-duty favor. So yeah...very pricey (Edit: but less than the cost of a trailer and a rooftop tent) but that's true of most things that are made well.