Minco has some tools to help you with the design parameters for your system. I would suggest starting at the heaters section of the public website.
http://www.minco.com/products/heaters.aspx
Download the design guide to help you through this process. The online configurator can help you find a model that might work to develop the needed characteristics of your heater beginning with some dimensional limits (rectangular or circular only).
Physical parameters of the maximum heater outline and any bending it may be required to do should be able to be within the scope of information you have from the mechanical design. For maximum thermal uniformity you will want to occupy as much of the area needing heat as possible and keep the watt density low so that there is more on time than off time required in the duty cycle. There is an online aid to help with calculation of an estimated wattage for warm-up which is usually the most demanding part of the heating cycle. Armed with some estimated power requirements and knowing the availability of different power sources will go a long way toward helping select a heater of appropriate resistance range. You will probably need a PID controller for maintaining a constant temperature.
If you can provide Minco with some specifics about your needs, an email to the "ask the experts" will get you some help, or get some engineering assistance by putting your zip code into this web page and calling Minco:
http://www.minco.com/contactus.aspx?id=157
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