I wouldn\'t bother if it\'s for the sake of the Youngbloods cattegory. The judges don\'t actually like plinths and the like, so you\'re better off just submitting the model just on a normal base. The guidelines say:
\"Many people like to mount their models upon large scenic display bases or plinths. This is permitted providing the individual model can be removed and stand upon an appropriate sized gaming base. If the scenic base is integral to the model your entry will only be eligible for the Diorama category. Although display bases can add to the impact of a unit, our judges do not take such bases into consideration when making their decisions. In fact models on display bases are usually removed from the base when being judged.\"
So you can use a plinth if you really want, but ultimately there is no reason to spend cash on one.