With SPF, those "reverse MX" records are easy to publish: one line in DNS is all it takes.
To get your SPF setup on XpertDNS you need to first setup one up with this SPF Wizard
When you are finished with the wizard there be an output of your SPF. There will also be an output for bind and tinydns. You will only need the actual spf record as in the example below.
You can then add a TXT record to your domain in the DNS Control Panel; add an SPF records as well for an SPF complient domain. Just paste in your SPF into the address field and click add, and that's it. You have setup your SPF.
More information about SPF is available here: http://www.openspf.org/