Donation integration is fantastic. However, the secure https pages redirect to the slug.nationbuilder.com address. We're using a donation page as the splash page, and the redirection in the domain name is confusing to users who are trying to make sure they're donating in the right place.
NationBuilder will implement SSL on all websites by February 1, 2018. This implementation should enable the use of your custom domain on your donation page while also maintaining SSL encryption. Please stay tuned for more updates.
Unfortunately, this is not something we can support as these pages need to be SSL, which is why they are shown on the slug.nationbuilder.com domain. Technically the way this would have to be implemented would require us to charge a significant monthly fee, more than what NationBuilder itself cost. And I'm pretty sure almost no one would end up wanting it at that price.