AIf I'm placing an RKT structure on top of a 6-inch cake, do I need to use dowels (or bubble straws) beneath the structure? I'm worried that the structure might be slightly too heavy for the cake.

AI always believe you are better to over-reinforce than under. You will never be sorry for having extra security, but you always regret the time you didn't put in the extra structure and something fell or collapsed.

y'know that sign at the dentist 'only floss the ones you want to keep' -- translate that into cake and it's 'only support the tiers you don't want to floss' or something like that