Can you apt-get with no internet connection?
If you jave the gcc Compiler and the associated tools, and SDL, installed on your Ubunutu, you only need the DOSBox source code. Self-compiled stuff is usually going to work best since it uses all the right libraries etc.
Try by typing
gcc --version
and also
sdl-config --version
into a console window, if both give you a version message (rather than "command not found") you probably have the needed tools.
The source is straightforward to use: Unpack it
tar xvjf filename.tar.bz2
cd dosbox-0.72 (or whatever it's named, see output of command above)
./configure
wait a minute
make
wait some more minutes
sudo make install
That's all. For more info read the included README file.