We 'inherited' a Lab cross sheep dog from my daughter when they moved into a flat and then they moved to London. He was still a puppy at 9 months old - more than a bit wild.
First day alone in the back garden he wrecked the place. Second day he finished the place off.
Third day in desperation I put him in the front of the van (has a dual passenger seat) and was as 'happy as larry'. Now he is ready and waiting at the front door when it's time to go to work.
In the early days if I went round the back where I couldn't be seen then he would bark a bit. I did put the pole down and come back to the van and talk to him. Once he had settled, I went back to the job. I didn't get much done those first few days.
Now 3 years later he doesn't worry if I'm away for an extended period - he's in the van and that's all that counts and I will come back. As long as he hears the pump he just sleeps. Occassionally he goes ballistic if another dog comes by, but I react as quick as possible if I hear a lot of aggressive barking.
Unfortunately you have to expect some dogs jumping up at the doors and scratching the paint work and you also need to ensure that you carry your van keys around at all times - in the excitement they can lock themselves in the van.
In the summer you need to carry a water bowl and you need to leave the windows partially open. I have also turned my van around so the sun doesn't come in through the windscreen even if not convenient, and put a towel up at the side window to stop the sun if necessary. You also need to be aware of the weather. A cloudy cool day can turn hot for a dog in a short period of time when the sun comes out. I do regular checks on him to ensure he isn't too hot - ie panting. He has a black coat and gets hot quickly.
At times I have used to opportunity to take him for a walk at lunch time on one of the many walking tracks we have in our area. So I carry a roll of poo bags with me in the van. I also carry a Hozelok spray nozzle that I can connect up to the hose port with the same hose I use for the hose reel and wash the mud off him. Also carry a towel especially to dry him off. I also have a towel across the front seats and just put up with the amount of hair this dog sheds. Regular hoovering keeps on top of it.
There can be times occassionally when its too hot to take him out. He then stays at home. He isn't happy, but its in his best interests.
And then in winter the van is the best place to be in. If it gets too cold then I put the diesel air heater on and keep the cabin cool to warm (18 - 20 degrees) while I'm freezing my butt off outside.
Having your dog around is good company, but will reduce your productivity, guaranteed. Customer's enjoy talking to him sometimes and I have also heard the remark often that 'I see you have brought the boss around with you'.
Customers see you as soft hearted when you have a dog, if you are a dog lover then you are OK in most people's books.
I never carried treats around - it would be my luck that I would teach him that barking is a way to get a treat.