You can do it using DVDShrink, heres a guide http://www.afterdawn.com/guides/archive/multiple_dvd_to_dvdr_dvd_shrink.cfm
I use something called DVD Copy (a tool for VideoRedo but not part of the program itself) to rip each disc into it's own mpg file then put several of them into ConvertxtoDVD which converts & burns a full size DVD. If I want to edit the video first then I use VideoRedo between DVD Copy & Convertx.
Assuming you don't have menus you need to keep since we're talking about miniDVD sources, I'd go with DVD Shrink i Reauthor mode. If you need to keep menus I'd recommend commercial software called DVDReMake Pro, which can keep multiple menus as well. Although I love VideoReDo (I've owned it for about 3 years now) it's not necessary for DVD backups unless there's editing involved. If you need to edit the video, and want frame-accurate cuts, I'd definitely go with VRD (VideoReDo). For GOP accurate editing you can stick with DVD Shrink.