I am looking to put a tub enclosure in, but have a window, would like to cover window up would it be a problem because of moisture and heat in bathroom and cold air outside. Do not want problem with window leaking or mold please help

Thanks

Rather than covering the window why not consider replacing it with a thermopane window. An exhaust fan will also help.

The best solution, if you want to cover the window, is to remove the window unit and fill in the wall opening. On the inside use drywall and insulate the cavity. On the outside, cover the opening with hardie or other siding like the rest of the house, If it is brick, more work but the same procedure

Do you mean you want to put the enclosure over the window opening? If so, I agree with ma0641. Close up the opening.