I split my api up into folders:
v1/resources/users.rb
v1/resources/orders.rb
v1/entities/order.rb
v2/resources/orders.rb
and then in api.rb just mount the individual files ...
mount V1::Resources::Users
mount V1::Resources::Orders
mount V2::Resources::Orders
And then:
version ['v2','v1'], cascade: true
version 'v2', cascade: true