My material is polycarbonate twin wall. Same stuff they make safety glasses out of. Chloroplast will split with paintball impacts. Taint cheap at $80 for a 4' x8' sheet which weighs 7.25 pounds. 1/4 plywood same size would be about 20 pounds a sheet.
Here is a cross section of how it looks.
Here is a pic of it up fairly close showing how I use Hot Glue to reinforce screw and bolt attachments.
I would suggest a PVC frame with the bottom covered with fabric and even painted and netting all on the top half. Make it a Box that works like a SLED so the bottom edge looks like tank tracks so you can drag it up over obstacles on the field. Use some 1/4" plywood triangles to reinforce the PVC at the corners and high stress joints. Rig up a belt so it works like a harness so you can pull it hands free. A crossbar in front to lift it up with. Maybe a two man? Remember there is a reason why the romans put the horses in the FRONT of the charriots. Make sure the horses in your tank are very forward in the shell and dragging it rather than trying to push it. maybe some roller blade wheels on the rear end of the track. One on each side of the PVC that is reinforced with plywood.
This design won't work but show what I mean by a box where the bottom edge is shaped like a tank track.
The occupant would have to be farther forward to PULL it. This design would be like pushing a loaded grocery cart through a gravel pit.