i also read online that a sealed enclosure flexes alot. and it is HIGHLY recommended to make 1" sealed. denser the wood, lesser the box flex, less energy lost, more accuracy...so lots of advantages.
1" mdf is as dense as it gets.
or
if not 1" sealed, than atleast the front baffle should be 1" or double up with two sheets of 0.75" (i did this for my twin sealed enclosure)..but this type of box where u double up needs very good construction so that the layers dont rattle /does not have play
these 1" enclosures must have cost a fortune :o here in pindi just the sheet alone costs rs3.5k...!!