The Department for Transport (DfT) is inviting people to submit their views about the 66-acre spot next to Junction 10a, which is being made ready for the end of the transition period in December.
When built, the site, officially called the 'Sevington Inland Border Facility', will be used to process paperwork before truckers continue their journey.
And in the event of disruption at Dover and Eurotunnel, it will be a holding area for up to 1,700 HGVs to avoid queues on the M20.
Now ministers are keen for residents to share their views on the project, which was shrouded in secrecy in the summer when the government snapped up the site and started construction.
Although 'enabling works' have been taking place since July, a Special Development Order (SDO) which allows the Secretary of State to grant planning permission still needs to be confirmed – and the 14-day public consultation forms part of that.
Residents now only have until Monday, October 26 to comment on the scheme, with the government saying any feedback received will "help shape details of the planning submission".
Ashford Borough Council (ABC) deputy leader Cllr Paul Bartlett (Con), who lives close to the site, is urging people to get involved.
"We have only got until the 26th and I think it is vital people go on the website - now is their chance," he said.
"This isn't a normal planning application where people will be able to go to a committee meeting and have a chance to speak, but it will be determined by the Secretary of State who will see the comments.
"It is an opportunity for people to put their view in front of the Secretary of State before the decision is made and it is rare to be able to do that.
"This is a serious consultation and people need to embrace it.
"It is not an opportunity for the Remainers to have a go at Brexit, but it is an opportunity for the people who want to genuinely have a say about the impact it will have on the community.
"The SDO does need to demonstrate that they have had a public consultation; this is an important part of that.
"We don't want people saying afterwards how they wish things were different – they have got to engage with it now."
As well as the 66-acre Sevington site, the government has confirmed the nearby Waterbrook Park industrial estate could also be used for lorry parking.
The park off the A2070 Bad Munstereifel Road is already home to the town’s truckstop, but ministers want to turn part of the estate into a contingency customs check site and “potentially for traffic management purposes”.
In a letter sent out last week to residents living nearby, MP Rachel Maclean confirmed the government is working on two Ashford sites.
“Alongside the Sevington site, HMRC will be seeking approval for the development of an inland border facility at the nearby Waterbrook site at Ashford,” she wrote.
“Both sites are being progressed to ensure that one of them will be available for January 1 2021, and the current intention is that the Sevington and Waterbrook inland border facilities will not be operational at the same time.”
Ashford MP Damian Green says the Waterbrook plan is an “insurance policy” in case the Sevington site is not ready for the end of the transition period on December 31.
He told KentOnline: “It’s just in case they can’t get the Sevington site up and running in time.
“There is no reason to believe that they won’t, but it’s a back-up.
“It would be much less good if it was used because it is further away from the motorway and it would cause a lot more inconvenience.
“I have been told they won’t both be needed at the same time, but I am keeping a close eye on it because we all know that plans can change.”
Cllr Dara Farrell, leader of the Labour group at Kent County Council, fears the Waterbrook site will be used.
The Victoria ward representative on Ashford Borough Council said: "They say they won't both be used at the same time, but this is the government that said the Sevington site wasn't a lorry park in the first place.
"Whatever they're calling it, there will be a lot of lorries on there.
"I think they need to be upfront with people about it and start the mitigation works now for when Waterbrook is used as well.
"We don't want lorries going all over the place."
The number of trucks able to be stored at Waterbrook is not yet known, but up to 1,700 HGVs could be parked up on the Sevington site for six months, reducing to 950 after July 2021.
On the Sevington plot, the northern section of the development will initially be used for HMRC customs checks from January 1, with the southern part close to Church Road becoming a holding area for lorries in case there is disruption at the ports.
It is expected lorries will continue to be checked on the land until 2025.
All vehicles accessing the spot will have to use Junction 10a and drivers will be fined if caught using other routes.
To take part in the two-week consultation, visit www.inlandborderfacilities.uk