Following up consistently is a challenge.
So, let's make this easy.
Automate it!
1. Create your email template. Steal this one.
2. Change the last line every so often - make it funny / playful / friendly.
3. Personalize the subject line, etc. This will increase open rate and response rate.
4. Set up the workflow so that a task is created, in a Task Queue. Send that email out 24 days (or so) later.
Know where you stand. Track losses. Ask for feedback. Record the evidence for your Lost RFP - RFI report.