These caskets were built to what the Funeral Director told me were the standard size for a average size long or short term tenant and to fit into their vehicles, I know mine did as I helped him load it into his hearse. Its specifications are LENGTH' 0000 mm WIDTH' 0000 mm DEPTH' 0000 mm  the edging around the lid and the base are standard shirting board, the handles are timber, while the casket sides and bottom is 12 mm untreated ply with the ends and lid being  07 mm untreated ply.                 
Although caskets and coffins are used for the same purpose, both can be used for underground furniture or for stocking the fire  they are two different features, a coffin is constructed with SIX side panels, a top and a bottom, while a casket is constructed of FOUR sides, a top and a bottom.
I made one for my Dad in consolation with the Funeral Parlour and Funeral Director that eventually use it, then two more for ourselves but have since decide ours may be a bit premature, subsequently here they are.
While I can not categorically say if you can fit some bugger into it the bottom will not fall out, something I would imagine  would be ALL Funeral Directors biggest fear when  using caskets  from a unknown source. However it is reassuring that the  guy who took care of sending Dads body on its way, told me that he used the SIMMONDS BUILT casket with absolute confidence that it would do the job.
These caskets are unlined as I was advised to leave the lining out as it must  be removed so as a government approved lining and a considerable amount of shredded paper is packed under the lining before the deceased is placed into it, however you can paint or decorate the outside any way you wish, there is also no reason why you cannot make and supply the linning material. 
Freight and delivery is the buyer's responsibility.