Some kennels specialise in small dogs and if he is not used to big dogs this can help, but I have small dogs and they love going to the kennels. They can bark at all the other dogs all they like.
Visit one or two to see what they are like, when you find one
book early as they get full up quite early on. Some people recommend taking him in for an overnight stay beforehand so they know you are coming back, although personally I don't think this is necessary. Take his bed and some toys or a jumper belonging to his owner and even his own food if they don't feed what he is fed on.
I have worked in many different kennels over the years, and can honestly say the owners worry far more than any dog ever does.
Remember most people who run kennels do so because they like animals, and it is their livelihood, so are unlikely to be uncaring or inexperienced.