I have implemented MercadPagos without problems, but, When with MercadoEnvios I have one problem that I don´t know how to resolve..
I have configured a simple product with the height, width, lenght, weight.. This variables were associated to the MercadoEnvios vars.. so, it should calculate the shipping cost without a problem..
But, when i fill the billing address form, in the end of the form where I can choose the shipping method, in the MercadoEnvios sector no show nothing and below appears a red error mesage saying: The MercadoEnvios is not avaible now...
Did you checked the Magento logs to try to see why the method is disabled (or not available)?
(Quizás te convenga levantar este tipo de thread en el foro en español y/o en el issue tracker del propio módulo)