The Gift shop [supporting Rupert's Fund, the Cavalier Collection scheme - both for research into Cavalier health - and Irish Cavalier Rescue] has these wonderful car harnesses which we use
They are excellent as walking harnesses too so you don't need to take them on and off when going out in the car. The panel is neoprene so dries very quickly.
It is comfy to wear too!
It has clips on both straps so you don't have to pull it over their head [which many Cavaliers hate ] Mine have learnt to hold their paw up to have it put on!]
You can also get the camo colours - this is the pink [of course!] - but there is also a blue camo
Something special for your Cavalier and supporting these wonderful causes too!