Clinton, Your box you are using now is fine in theory, because it is hollow so your harp will have more resonance than any 4 legs would have. However, I see several ideas to consider.
If you want something more elegant than your box, with the same color wood as the harp, have an experienced instrument maker make you one after careful measurement to allow for your height when sitting, and arms outstretched to the middle area of the harp strings. The harp might be able to attach to the box by two small devices at the sides. You might opt for small wood strips on top of the box so that the harp is confined between strategically placed strips while you are playing. If you wish to leave the harp standing alone when thus modified, it would not be safe unless part of that box-base extends outward or has extensions like four flat “feet” and covers more floor area. To play with the bottom part of harp or box on wood floor instead of any rug, will certainly give you more tone but there might be some compromise needed. Talk to wooden instrument makers, and even investigate stands already made to receive instruments like bowed strings, which certainly could not be stood on end without the wooden, velvet-lined rectangular ones available for violins, violas, cellos, and basses when they are at rest. Shar at http://www.sharmusic.com or 1-800 287,7427 large catalog of 143 pages carries those, and in my free print copy(fall-winter 2011) I see a picture on page 82 of “classic hardwood cello stand” at $149. I have one, for a cello, and cover the instrument with a clear plastic cover (from dry-cleaning a shirt or jacket) against dust, but it can still be seen, and always ready for immediate playing rather than locked in a cello case. Perhaps others will post here with better ideas!

Clinton, since my stand and cello are at a student’s home I cannot measure the stand interior. After measuring the bottom of your harp as it is now, you could call Shar and ask the interior dimensions. Their stand was not intended for use while a musician is playing. It seems to me that the sides of the stand might prevent your using lower strings if you set your harp inside it, whether tilted or not. Perhaps a modification of the stand would work, or a box-like base under your present harp would work; I am not smart to figure out that adaptation. Dusty Strings makes 34-string harps, in their Seattle workshop. Ray Mooers, the owner, is very knowledgeable and might know the perfect answer. The number is (206) 634-1662. If you were to call and ask for a toll-free number and after hanging up the phone, a more lengthy call on that new number would not be billed to you. Do you think you may wish a harp some day with 36 strings,(a C string at each end?) There are many models of those made these days and they might suit your height comfortably, sound more resonant because of larger sound chamber instead of adding anything, and finally,,they all stand alone safely without needing any extra stand..It bears thinking about, instead of some costly adaptation. Best wishes to you!