So I'm trying to add a class to the form element and the form is generated using the following code:

@using(Html.BeginUmbracoForm<SearchFormSurfaceController>("HandleSearchForm"))

I've tried doing the following: 

@using(Html.BeginUmbracoForm<SearchFormSurfaceController>("HandleSearchForm", new { @class = "myclass" }))

This doesn't throw any errors however doesn't add a class to the form element.

To add a class to a label for example is easy: 

@Html.LabelFor(model => model.Weight, new { @class = "myclass" })

Thanks.