Local Plans are not my forte but isn't there a snag with objecting to the HMRC facility, either outright or to ensure it remains temporary, inasmuch as the site is part of the White Cliffs Business Park phase III? C.f.
https://www.dover.gov.uk/Planning/Planning-Policy-and-Regeneration/PDF/Land-Allocations-Local-Plan.pdf.
Assuming that's right, then the two bits I found concerning it are 3.46 and 3.47 (Policy LA2) which provide/stipulate protection for the North Downs Way and 25m of bunding and dense planting to shield houses on Dover Road.
Apologies if that's either wrong or well-known already.