No guide for DOSBox installers per se, but just learn to use one of the installer scripting systems. I use and highly recommend NSIS and I do a lot of DOSBox installers. In fact, GOG has used many of my installers and other resources for their Sierra releases with varying levels of my direct involvement. NSIS is free and very well documented. It is very flexible and robust packages available. I have found everything I have needed on the Wiki or forum. I have only ever had to ask for help a couple of times over the years.

What I am doing is more complicated than what GOG does in that GOG will design a package using an included set of files. My installers do not include that games themselves and have to take into account a range of different versions or releases that a user might have. They have to be able to identify the original media. I also have to duplicate the tasks of the original installers by concatenating resources spanned across several floppies, extracting files from archives and or expanding some of the larger compressed resources. They also apply all of the relevant patches, but some of these may be binary level patches that shipped with some old 16-bit DOS patching utility.

Depending on the game, an installer may be very simple or fairly complex. There is an older IDE for NSIS called NIS Edit. It is getting to be a bit long in the tooth, but it does include a wizard that can guide you though scripting a basic installer. Just change the selected user interface from MUI to MUI2 (in the includes).

There's also Innosetup which GoG uses.

Different learning curves definitely do apply. Both are script based, though NSIS is very bare and is busy upfront which can be daunting. That said i'd love to switch to NSIS for my things some day, if only my installers could look just like mid-90s Installshield/Wise's...

NSIS does have a bit of a learning curve, but is really not that hard. It is extremely flexible and powerful. The basic stuff is very straight forward. i.e.:

1  SetOutPath "C:\MyGame"
2  File "My Game.exe"

Will pack the file "My Game.exe" in the install package and extract it to "C:\MyGame".

1  Delete "My Game.exe"

Will delete the file "My Game.exe". Just simple commands. It does allow for more complex operations, such as playing around with the stack, mathematical operations, searching, downloading, string manipulation, file manipulations (changing, appending, reading, checking size, MD5, modification date, etc.), conditional statements, reading files, manipulating the Registry, interfacing with the internet, etc. Its scripting style is said to be a bit like PHP and assembly. You can even use it to write some simple programs, as many have done. One of the default plugins is the system plugin, which allows for all kinds of calls to retrieve information about and manipulate the system. It is deep enough to still be usable as your skill with it grows.

As to how bare bones it is, it, like any other installation package is mostly scripting. No matter the system used, by far most of the time will be spent staring at text, writing your scripts. There are several IDEs available, some providing more of a graphical interface than others, but the installer's UI can be just about what ever you want. Some IDEs will let you design the UI with the ease of the form designer of VS. You can mimic other installers, if you want, even Inno Setup. One thing that I dislike about Inno is that it is more of a hassle to examine the contents of an Inno installer, but far from impossible. Just none by shell extension. Several utilities allow you to do so, including the installer script. An NSIS installer can be unpacked with 7zip, though with no usable script.

Just checked this out, it's awesome

It is just an alternate UI for NSIS. Outside of the retro look, was there something specific that caught your eye?