Header and footer templates for email newsletters using mailchim

Hi there,
We are an online based guitar strings, spares and accessories retailer (stringsdirect.co.uk). Up until now we have been sending e-mail newsletters using the the platform within our website hosting client. However, we have now moved over to sending e-mails by Mailchimp. We need a newsletter template with consistent header and footer to be created with the ability for us to design our own content that we can drop in between.
We have an in house designer who designs the e-mails, however, they only have minimal coding knowledge so are unable to create the header and footers we require.
Look forward to hearing from you soon.
Lee
Strings Direct