There are several methods to customize fdubcd.img so to have more space available. But IMO, making a bigger image should be your last resort, considering that it affects other entries in the Syslinux menu and that it slightly reduces the chances to successfully boot.
One possibility for you would be to reduce the size of certain cab archives (inside fdubcd.img) which contain "dispensable" files.
A second possible method is to copy fdubcd.img, delete the programs and cab archives that you don't really need to be available simultaneously with your customized programs, add your additional tools and set a new menu entry. You end up with the original fdubcd.img and with an additional fdubcd_custom.img.
The easiest method, if you don't need simultaneous access to your custom DOS programs and to other DOS tools, is to add a new image with your customized DOS tools under
, adding a custom entry in
for that image.
Note: when I say "simultaneous" I mean that for some reason you "must" have access to several DOS programs without rebooting UBCD.
The adequate option for you depends on the required additional size, on the real needs, and perhaps on your own knowledge.
2. In the customization doc it is stated that zip, rar, 7z, uha are supported but for me it works only with cab.
I haven't "played" with the other archive formats in fdubcd for some time, so this needs some testing. Thanks for reporting.