How to send an offer for owner financing?

[Khadijah Celestine]

Link to The Letter

I want to send an offer to a house that I've seen. 

The Deal

Baltimore City townhouse

Asking $50K 

15K down owner financing

10% (annual)

Fully amortized over 5 years

The Offer

$30K purchase price

$10K down

15% interest (annual) 

Paid over 3 years fully amortized

I want the offer contingent on inspection. I also want to protect my interest in the property and I'm not sure how to do that. I've heard of something called "holding the title" which will offer me complete control of the property while the sellers hold the deed. How do I add this? Should I send a letter of intent? Would that count for anything? Please help! Thanks in advanced.