I cant for see any real problem with them jrussuk as long as you have hood etc sorted to your taste. One of the dimensions you stated would be just like a 5'x2'x2' just shorter and there are no major issues there, you may want to consider though cleaning the bottom of the tank, if you can get all round access you should be fine but front, or front and one side only may be difficult at the back without a long syphon
just my 2c
Andrew