Booster seat install

[sarahs]

My 4.5yr old ds rides in grandma's car once every couple of months. She has a Cosco convertible and a Cosco combo seat and he has been harnessed in the combo until now. He is now over 40 lbs and I have stalled putting him into the seat in "booster mode". He is harnessed in all other relatives cars (marathon, husky, apex) and I prefer that, but he rarely rides with this grandma and only for very short distances.

This is my first experience installing a booster. Do I really JUST use the seat belt to "buckle" in the seat? I mean, what holds the seat down when she is driving around and no child is in it? It does not appear to have a teather. Do I have to remove the harness?

My other issue is that I have 2 yr old twin daughters and grandma really wants to be able to take them on short trips to the store, ect (why I don't know!). Can I leave the harness on the combo seat and not use the harness when ds rides in it (booster mode/using the vehicle seat belt to strap him in), then having it usable when dd rides in it. Of course, I would have to thread the vehicle belt/install the seat each time, but it is easier than rethreading the harness each time. Is this allowed?

Thanks so much!

[Joolsplus2]

Yup, the belt just goes over the kiddo and holds him and the seat down... it's very odd to get used to!
You are technically supposed to remove the harness when used in booster mode, but if I were facing that situation personally, I'd be inclined to leave it in and reinstall it for the 2 yo as needed (the manual doesn't say it's ok, it would have to be a parental decision...technically you have to remove it to lower the weight of the seat to meed a 9 pound guideline, but there are many boosters that weigh more than 9 pounds and there's no enforcement of the rule at all, just so you know why they say that :) ).
I would also be inclined to go ahead and get the 4 yo a nicer booster, as the Cosco tends to make the lapbelt ride a bit high and the shoulderbelt not touch the shoulder...and you're going to need boosters for the next 8 years or so, anyway (the Parkway or Compass or Evenflo Big Kid are very grandma-friendly, I think).

:)
Julie CPS Tech and mom to 3 in seats
http://www.cpsafety.com/articles/RFAlbum/SarahMA.aspx