
I bought them last year and they're ok. I had the larger size (x2) which I found a bit bulky bulky to put in the fridge (for the same reasons as you....OH seems to know about some impending famine that the rest of us don't :rolleyes:). I found they needed to be 'refreshed' pretty frequently but were fine for the job on very hot days. My two aren't chewers but I don't think they'd withstand a dedicated chewer ;)
I now have of these
canine cooler beds which Lola chooses to sleep on most nights (even in winter

). I did have to buy it in from the US as I couldn't find one in UK. As it's water filled (21 litres in the largest size) it is difficult to move around but is great if you just want a cool spot in the house for Storm to lie. The bumf that comes with it gives details of filling with less water for use in the car etc and the smaller sizes will be lighter again, of course.
If you are just looking for something to help keep him cool in the car on hot days, I'd stick with the thermo thingys as the canine cooler really isn't that portable but the benefit of it is that once it's filled, that's it. No more soaking, refrigerating etc. :)
Probably not that helpful but there you go :D