Help me decide on harness or booster for a trip

I'm taking all 6 kids to visit relatives in MO this summer all by myself. It'll be about a 12 hr drive give or take.

Kaleigh Grace will be 5 yrs, 10 months old by the time we leave and she already weighs 45+ lbs.

She rides harnessed in a FR 85 with me but in a TB with her dad who has her every other week. She also rides in a booster on the rare occasion I take her somewhere in my car.

As far as I can tell, she does well in it. She's fallen asleep in her PW before and stayed in position. She sits in the 3rd row and I'm considering letting her ride in a booster simply for the ease of getting 6 kids in and out of the car. It's a lot easier if I don't have to crawl back there to buckle and unbuckle her. Yes, another kid could do it, but she prefers I do it. The boys get kinda rough with her. She can do the booster by herself or at the very least undo it.

She'd be riding in a ProBooster because it's the only thing I've found that works with the weird belt geometry back there. I don't have one, but I tried my friends and it works. I don't know if it will be tippy because I didn't try to drive with it, but I figure I'll order from Amazon and if it is I can send it back. The Oobr does too, but I don't have the money for that right now. The PW she has doesn't let the belt retract.

What do you think? Would you booster her for ease of pit stops or keep her harnessed? Another plus would be that I won't have to try to pack around her tether if she's in a booster.

BUT She's one of "the babies" and I'm not sure I'm ready to let her grow up yet. Kaleigh and Caleb are 17 months apart and I still refer to them as "the babies" sometimes. lol Plus CJ might throw a fit about being harnessed if she's not. He rides in a booster with his dad so he thinks he should with me too. It helps when I can say Kaleigh's in a harness too.

Can she buckle herself? My dd2 has been buckling herself since she was 3. She rides in a fr85 in the third row of my Yukon xl and I never have to crawl back there unless she falls asleep and I have to get her out . Otherwise a booster is fine if she rides good in it.

I don't know. I don't think so. She's finally gotten to the point where I can get her to put her arms in and do the chest clip while I'm buckling her brother. Before she waited for me to do everything.

I'll have her try when she gets home Friday. She's at her dad's now.

I'd leave her harnessed because of sleeping. Do you have experience with her sleeping for extended periods of time? IME, even good booster riders may not do great while they're in a deep sleep. There's no getting out of position in a harness. My 7yo DD is a fantastic booster rider, BUT she sleeps curled up on her side so when she's really out she reverts to that and also tries to pull her legs up by her chest.

Can you start having her practice buckling the harness now? Don't adjust it and it will be easy to quickly check.

Harness. Also you won't have to worry about her staying in position on the long ride, especially if she sleeps.

I'd keep her in the FR85 and I bet she can buckle herself in-she just wants you to do it. The Regent was really hard for K to buckle-but once I realized he could do the Nautilus easily I started encouraging him to do the Regent by himself.

Harness it is. Thanks!