Sadly the nearest would be Dornoch - about 70 miles from Clashnessie. But it's a lovely strip, and a nice drive from there to Clashnessie. Don't know about car hire in Dornoch but you'll usually find a local garage that'll rent you something. And light aircraft to Dornoch plus car hire is MUCH nicer than commercial to Inverness. No hangarage or security at Dornoch but in the past I've popped in to the local police station and asked them if they'd mind keeping an eye on the plane - they were delighted!
Alternatively you could go to Dickie Bird's strip at
Easter, which is tucked away from public view and Dickie will keep an eye on your aeroplane. A bit further to drive to Clashnessie but not much in it - and Dickie will advise you on car hire.
Haven't been to Clashnessie since 1968 but it's a beautiful place. Have a nice holiday!
NS