Hi Gregory
Was this the first time you had left him? He may have become distressed at being left for longer than normal. Was his tray already full? Cats are very fastidious and some will only use a tray that is relatively empty. You might like to add a few other trays if he does not have excess to the outside and make sure they are clean. However, overly clean trays can also be off putting so leave a tiny bit of soiled litter in there so he is familiar with it.
Clean the areas with biological washing powder and spray with an odour eliminator. Cat urine can be very difficult to remove and once the smell is there can encourage cats back to that area. If you can remove the covers and wash these that would be a good idea and if you have to leave him again cover these areas with something like tin foil (aluminium foil if in US).
If he continues to urinate inappropriately seek advice forma qualified behaviourist recommended to you by your vet.
Good luck
Al the best
Rosie Barclay