From: "Anthony Mattke" <a dot mattke at gmail dot com>

> Is there somewhere where I can download an image of monowall with
> serial console support enabled by default for generic-pc ?

The RADIUS images that Jonathan De Graevehas been building 
http://inf.imelda.be/downloads/m0n0wall/ have that option.  From his 
features.txt

NOTE: Images with serial are compiled with serial console enabled and with 
kernel parameter: kern.ipc.nmbclusters=32768
This assigns a network buffer of 64MB kernel memory. This enables the 
ability to handle a great amount of connections.
If you use the serial image, please consider that you have at least 256MB 
ram and I recommend 512MB or you could get a KERNEL PANIC or run into a 'out 
of memory' situation.