Superphil
Dismember
Seaford away to Selsey? Not been but a long drive for non league
I think you have the two extremes of the county there, it's only 50 miles or so, but yes, probably as far as any away trips in the Combination League.
Edit: just checked, Little Common and Bexhill United are further away from Selsey than Seaford, although they are both in the Premier Division so their longest trip would be to Pagham, 70 miles.