ok so i am designing my new enclosure to house my future purchase of a scrubbie, having some thought issues with heat though, the enclosure will be 2400 x 2400 x 1200/1800, so heating a large enclosure has to be hard, i am building a light hutch for the top of it so i dont have to be in enclosure to change heat lights or daylight lamps, dont like the idea of being in an enclosed space with a possible hungry large snake

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firstly can my fellow aps friends help me with suggestions on heating this behemoth, i was thinking 4 x 100 watters on one side in light hutch, but as i have no experience with large encs i have no idea if this is to much or to little, do i need to supplement the heat with maybe heat cord under tiles or something like that in the bottom.
secondly this enclosure will be kept under my back verandah, i am in melbourne and the nights can get pretty chilly, i am thinking of putting some rubber sealing strips around the doors so the enclosure will pretty much be air tight except for vents, am i going to have problems heating this enclosure in cold conditions and keeping it to an acceptable level.
there is some scrubbie keepers in vic, and i beleive that some of you keep them in aviarys outside is this just with heat boxes?, if so doesn;t your snake just sit in box all the time?
and what about humidty for scrubbies, i know that chondros need humid enclosures and scrubbies come from similar enviroments, can scrubs be kept a little drier or do they need massive humidity.
i will post some pics of my ideas soon, i am planning to do a build sheet for this enclosure if i build it successfully.
please help me i am doing my head in atm