I normally recommend American Securities CSC series safes for customers looking for something smaller than gun safe height. These safes are made of 2 layers of 1/8th inch steel and between those two layers they have a concrete like composite fill. It is also equipped with a glass plate behind the mechanical lock. This glass plate is connected to a cable that ties it to the relocker making it sensitive to a drill or punch attack. There are 4 sizes. The models are csc1413, csc1913, csc3018 and csc4520 in order from smallest to largest. The largest csc4520 is large enough to accomodate long guns with a special interior. Here's a link to give you an idea of what they are
http://www.thesafeplace.com/commercial-safes/