Hey,
I have kept Drymarchon in all manner of containers,from Neodesha plastics to melamine and molded injected plastic cages( (Read:Visions) I personally like the plastic cages:Bottem line, easier to clean and easier to move around. At the size you indicated your Drymnarchon were now(I beleive you said 4.5 feet in length) you would be well advised to move them into 6 foot plastic cages. The four foot cages wil suffice, to be sure, but you will end up spending twice again the amount of money for another set of cages when these snakes hit their maturity and grow into the six foot range.Larger cages,in my opinion, allow the animal much more room of movement,and I have found the incidence egg binding in Couperi that are kept in large(6ft or larger) cages to be lower than those in 4 foot cages. This is just an observation that I have made and 'Im not sure if the other fellows here would concur.
Haveing said all that, the six foot cages have SOME drawbacks. Visions 6 foot model lacks structural integrity, and must be kept in a homemade "Rack system" or the cages buckle under the weight of the cages or anything substantially heavy placed on top of them. They also come in diffrent depths, the deepest ones can be a true pain to clean ,especially the BOTTEM cages. Habitat systems used to make some *Really* nice cages, not sure if they are still in business. I have used plastic, mainly visions with good results. Buy 6 foot cages for your Dry;s, youll need them eventually anyway.
*Cheers*
Fred Albury