For bike-rack compatible applications, you could tape together 4, 1/2 inch foam core panels to make a large square monolith. If your artwork is light enough, use pushpins for support. The panels come 4 x 8 foot, would advise cutting them down to about 80 to 84 inches high. Depending on your bike rack, you could also cut them in half so you had 40 x 48 sections, bring more tape. Use lotsa bungee cords for transport, those things are kites!
If you want to go upscale, sew together a big fabric sock that fits over the whole thing. Use Pic N' Save closeout bed sheets. Have seen this approach a few times, it doesn't look too bad. But as Justan points out, it won't please the fire marshall, although I have never seen anybody shut down for those reasons.
PS, that setup is way too light to use outside in the slightest wind!
Or you could use "U" folded foam core sheets on top of your tables. Just like at a science fair.
Other than that, just put a big tent inside your space.
Or find somebody who will rent or loan their ProPanel setup, transportation included.
Or put together a big frame of 2x2 lumber, use string as you did with your original tent. With long screws and wing nuts placed in pre-drilled holes it might be not too aggravating to set up and tear down.
But honestly, if you're gonna do shows, sooner rather than later you will need a nice display booth, which unfortunately will require a pickup truck or preferably a van to transport. ProPanels are the first choice for indoor shows, but the wire panels can stand up to outdoor winds much better. And the big white cubicle tents are nice too until the first tornado or 100 mph thunderstorm downdraft shows up.
Google "display panels" in Image mode for some good ideas. A zig-zag setup with taped-together foam core panels is another lightweight possibility.