Awesome responses, thought this thread was going to go nowhere after it was moved from the Centerfire section.
Ok - have it figured out and wouldn't leave you guys hanging on the conclusion.
My particular safe is too deep for a prefab cabinet (those are like 21") or vinyl wardrobes.
A visit to the Home Depot has revealed this:
Using three pieces which Home Depot will cut to size, I'm going to build left, right and top walls. Will cost around 120 bucks in parts for everything.
This will cover everything but the front so I'll need to fashion some kind of door that can take a lock.
This should obscure the safe from everyone outside the garage and anyone who wanders inside the garage so it should be ok if the garage door is left open.
Inside the custom cabinet I'll have a sensor that triggers if the house alarm is activated.
I'll also put a smoke detector above the safe that will go off if any heat generating tools are used.
It won't be easy to find or break open this safe but it will also make it difficult to access for me as well so I would recommend a separate safe for quick access weaponry for HD situations.