I have created a cart design based around a 27C080 EPROM. One full Mbyte can be used for data storage accessable from every code position. 768 KByte can be used for code execution. Read more about it on my MegaCART page. A similar cart with flash ROM is in development, too. It is called FlashCART.
Here I present cart PCB designs that fit into standard Videopac cases. You can use them to produce carts of your own software. Currently there is only one design here, it's a design which uses the maximum possible ROM code space without additional logic. All other carts without additional logic can be mapped to this type of cart, but you waste some ROM space by doing it.
If you want to create your own PCBs you can use the postscript files to etch your own PCB. As the design is double sided it requires some experience with PCB etching before. I have built my carts this way.
Another way to get PCBs is to use one of the many PCB prototype houses. They most likely want the Gerber files. I have not done this, so here you are on your own. If you go this way, please give me feedback about how it worked and about any problems you ran into. The outline is more complex than normal PCB outlines, so this could lead to problems.
For most uses I suggest using a socket for the EPROM. This is a problem, because UV erasable EPROMs in a ceramic case are too high to fit into standard Videopac cases with the normal sockets I could find. This is not a problem with OTP plastic EPROMs. A solution to this problem are carrier type sockets. They are much more expensive than normal sockets, but are low enough, at least the type I used. The bigger holes (1 mm) that are needed by the carrier type sockets are already incorporated into the PCB design.
Using 3K per bank means that the full address space 0400h-0fffh per bank contains program code. The EPROM is connected 1:1 with all address lines. This is not compatible with the way most commercial games use the Videopac, they normally use 2K per bank. Using only 2K means you don't waste (EP)ROM space, which gets expensive if you produce big cart runs.
The BIOS always occupies the first 1K in every bank, so this space can't be used. This is not really a waste of EPROM space, there are no EPROMs with 3K/6K/12K, so we have to have some unused space. It is possible to add an address decoder and use 2 EPROMs, but that is much more complicated and expensive.
This design is for a 27C128 EPROM. It supports 4 banks with 3K per bank, the maximum address space available for program code on the Videopac without additional bank switch logic in the cart. This is the type of cart that is used by KTAA. You can also use a 27C64 EPROM, but you only get 2 banks then. Using a 27C32 is not possible, the pin out is not compatible.