heating encloser

[Steele]

I was wondering how am i suposed to heat a home made encloser ? I live in canada so i need stuff that I can get here I am mostly woread about fier what clerance do i need for the heater will I have to put it in the encloser or can it go under the wood?I dont want it in the tank.I am bilding it frome melimine I am not overly conserd whith price I want the best for my boy and I want good quwalty so it last fore a long time. Thankes for the help