yep thats right rogan,
mdf(medium density fibre board) is made from wood pulp and glue, all compressed and dryed,chip bord is the larger 'chips' of wood glued and compressed together.
but be warned! both will swell and can crack tanks ,the poly can only even out so much,all it takes is a smal ship in the vanier and the water will get in.
because of the way its made,when the water soaks in it returns the fibre to how it was before it got compressed.
mat if you think there might be any give in anything,make sure that you add plenty of bracing!!,even go over board if you have any doubts,one center brace to me dosent sound enough for the whole stand.
Tim