getting married secretly

My fiancé (he's 26) and I (I'm 20) got engaged two months ago, we decided that it'd be best to get married once I finished college and he finished his contract with the marines. My parents think I am to young to get married right now so they were okay with our decision. 
Lately we have been talking about getting married legally now and get married by the church again once I graduate. This is because we are in a long distance relationship and him being in the military would help us save a lot of money for the future, I would also be able to have health insurance, discounts in flights and hotels, discounts in car insurance, and he would get paid more. 
I know my parents wouldn't think I'm making the right decision and would probably tell me I'm rushing things. I'm afraid to talk to them about it because it's very important for me to have their approval. We have thought about getting married in secret and never tell them, but I feel that I wouldn't be able to keep the secret from them, we are a very close family and I think they should know if something like this happened.
What do you guys think I should do?