The plan is (when we get the bongo) to take him with us most of the time. We have a large dog crate which he is quite happy going in, which will be ideal for travel (maybe bungeed to the front seats to stop it moving?)
Once on a site he could be tethered or in the crate in the awning, he'll probably sleep most of the time due to the walks he'll be going on.
The only worry I have is if we decided to walk to a local pub for a meal - if it was a hot day we could take him with us and eat outside, but if the weather was cool he isn't the type to be suitable to take indoors (even if the pub allowed) - he is still too young and bouncy!
This part of my question will probably sound quite bad

What are bongos like for leaving a dog in for an hour or so? Obviously in a normal car I wouldn't like to do it but what is a bongo like for heating up? Can you partially open the sunroof for air flow? Close the blinds and put the silver things on the windows to keep the sun out etc?
Do they have alarms? Can you disable the movement sensors?
Does that make it acceptable to leave him in the bongo in his crate (with water)?
Wouldn't want to ever endanger him but would like to make sure he is somewhere secure too.