contiboard is good for dry vivariums. Try local DIY shops who will cut to size, may deliver and will probably be cheaper than B+Q. At B+Q it comes it comes in widths up to 2ft and lengths up to 8ft. You could use hardboard or ply for the back, but it may be good to line it with vinyl tiles or similar. Seal everything with aquarium sealant. Predrill holes for all screws. One or two people on here sell air vents and glass runners.
It's much easier than it looks
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