I can't get a good RF install

[Adaline'sMama]

in my 2004 Honda Odyssey :(  I bought a van specifically so that I could RF my LO longer. The back seat doesnt have LATCH, so Im having to use the belt. No matter which side I put it on it wants to tip over sideways if I were to make a sharp turn. I put a pool noodle underneath, and it corrects the angle problem, but it doesnt keep the seat from tipping over. 

DD is almost 3, but only 25 lbs. I was really hoping to RF her until she was 4 or 40 lbs (likely 4), but if I cant get a good install, Ill have to turn her around. We rode FF home from the hospital with the twins because I couldnt get a good RF install, and since then we havent gone anywhere. I have to take all the kiddos to the doctor tomorrow, and she's going to have to ride FF again if I cant get it installed. 

Any ideas?

ETA: I cant install it in  the middle because I need to sit in the back.

[chickabiddy]

Do you know how to use a locking clip?  Installing the seat with a locking clip is likely to solve the tipping problem.  Let me know if you need instructions.

[Adaline'sMama]

I don't know how to use one. Also, is there a retail store where I can buy one or do i need to order online.

[chickabiddy]

What seats do you have?  Most seats come with a locking clip on the back of a convertible or the base of an infant seat.  (Locking clips are interchangeable, since they attach to the vehicle belt and not the carseat itself -- you can take a clip from one of your babies' seats and use it on the big girl seat if you need to.)

There are instructions and pictures at the bottom of this page: http://www.carseatsite.com/lockingclips.htm , and I think there's also links to videos on there too.