If the panel is rectangular - or at least one with multiple straight sides - you can use short battens of the length of the sides. Nail or screw them down to a board so that about one half of the panel is contained. So if it is a rectangle, two sides will be enough. If it is six-sided ,three pieces would do.
For ease of assembly, a copy of the cartoon should be fastened to the board first and then the battens fixed on top of the cartoon. The pieces can then be placed against battens and held there with pins or nails until the next pieces are ready.
Some prefer to tack solder the pieces together as they foil. This can be done in combination with the use of battens. However, leaving the soldering iron idling while foiling and using it only occasionally is very hard on the iron's tip and your electricity bill. I prefer to assemble the whole and then solder all at once.
For circular or irregular shapes a slightly different approach is required. You can use multiple pins or nails along the perimeter to hold the foiled pieces together. An alternative is to cut a piece of scrap window glass to the shape of the external perimeter of the panel. Hold it is place with nails or pins and proceed as with a rectangular shape.