I ended up using the padrino-contrib
gem. With it, you can install the plugin you need (of course you can do it manually also):
padrino-gen plugin exception_notifier
Which will add it to your gem file and also edit your app/app.rb
and boot.rb
files to load this gem.
Then in app/app.rb
you put something like:
register Padrino::Contrib::ExceptionNotifier
set :exceptions_from, "noreply@domain.com"
set :exceptions_to, "your_address.domain.com"
And that's it.
The nice thing about letting the plugin install it for you is that if you're more familiar with Rails than Padrino (as is my case) this will not only set things up for you, but also show you were the directives need to go.
Hope this helps someone else.