Namecheap domain not masking URL when redirecting to Heroku

Question

I have a domain with Namecheap that I am attempting to redirect to a Heroku app.

It currently DOES redirect, but does not mask the URL. (So visiting www.customdomain.com redirects to app-name.herokuapp.com, but then the URL stays as app-name.herokuapp.com instead of being replaced by www.customdomain.com)

I have followed this tutorial: https://devcenter.heroku.com/articles/custom-domains

So I have Heroku set up with the custom Domain. When it gets to the step mentioning a DNS redirect, I then attempted to follow this tutorial:

https://www.namecheap.com/support/knowledgebase/article.aspx/9737/2208/how-to-point-a-domain-to-the-heroku-app

This used to work, but I recently HAD to change to use Web Hosting DNS, and if you notice the options they mention for redirecting, that is not among them (This is copied from the tutorial: 5. Now you can start configuring your domain from Namecheap's side if it is using our BasicDNS, BackupDNS, PremiumDNS or FreeDNS.)

So I have access to cPanel for my hosting account, which I used to get it redirecting, but not masking the URL, as it did before.

I figure I have to do something else with cPanel, but I'm completely unfamilar with DNS type issues. Anybody have any ideas?