If you want a responsive page, and the form to be responsive as well, AND have a unique form on the page, then you need to create a responsive LP TEMPLATE, embed the responsive form in the code of the responsive template. Then create create a landing page from that template with editable sections and it's own css file as well that overrides some of MKTO's crapy css...
Alot of mucking around, but when you get it right, very satisfying. I think MKTO work off the basis of; nothing worth having comes easy 😕
Example: http://info.gettheworldmoving.com/wellbeing-incentives.html