Our older GSP male barks excessively in the car, ever since we got an estate car and he was caged in the rear boot area. He won't settle until we're doing over 60mph in a straightline (ahhh the joy of motorways), but as soon as you slow/manouvere etc he starts again. I was thinking of getting one of the collars that spray a little blast of compressed air when they bark. Has anyone had any success with these. Strangly our pup just sits there and watches him barking, with a look of disgust on her face!!

I have used both a collar and a water gun and both work, think the police would prefer the collar if you travel alone but I prefer the water gun but you need a willing shooter with you.

Edit to say it could be he is finding it very bumpy or painful at the back perhaps a thicker bed may help

I would certainly try to get to the bottom of why he is doing this as if it is fear based the worse thing you could do would be to spray him. 

My Sprollie was doing this when we went out in my van to go to agility training or to a show, as soon as we slowed down he would wine and scream with excitement or if I took out my other dog first to train him he would howl the place down.  We did use a compressed air collar.  I only needed to use it about 3-4 times before it stopped it dead. 

I had it too when arriving at a show.  The spray collar worked straightaway.

Our breeder recommended the water spray, but I tend to travel to shows etc on my own and thus spraying is not really an option, unless I practice over the shoulder target squirting
I don't think he's uncomfortable, the base is very well padded and there is vetbed like material all around the sides to a height of 8 inches or so, so side protection is reasonable. Maybe its too bumpy, the suspension on the car is quite hard. I guess it could be a fear thing as suggested, but he never hesitates to get in the car, and is very happy sitting in there when stationary/at open shows etc. I know he associates going in the car both for walks and to shows, so it could be an excitement thing?
Maybe he just feels car sick, but hes never ever thrown up in the car?

Can you get DAP diffusers for the car?

thanks for all your suggestions everybody, I will probably give the air collars a try.

>Can you get DAP diffusers for the car?

You can get a DAP spray, or a DAP collar.

Can he see more in the estate car than in your previous car? Might be worth 'blacking out' the windows so he can't see out until he gets used to it.

you can get spray collars that are activated by remote which is what I used, means then the dog doesnt associate it with you and also isnt set off by other dogs barking etc.

Yeah, try blacking out the windows that he can usually see it from.

That might do the trick.

That's really useful advice.  Basically, my patterdale doesn't like cars, she cries constantly except for a few weekends ago when we took her for a day out and came home in the dark.  I didn't put 2 and 2 together and realised that because it was dark, she was quiet, I just thought that maybe at last she was getting used to being in the car.  So I'll consider blacking out the windows.

an alternative is to have dog in a crate and cover that - much cheaper option