Raab stepped down as Brexit secretary on Thursday saying he could not accept the terms of the deal done by the Prime Minister.
He told the Sunday Times the UK should demand an agreement that allows it to unilaterally leave any customs union.
He spoke after two opinion polls suggested the week of chaos in Westminster has badly dented the Conservatives' election fortunes, with the Tories now trailing behind Labour.
Although there is still speculation in Westminster Theresa May could face a confidence vote, one of her ministers said there is still time for "more to be done" on the Brexit deal, despite an EU summit scheduled for November 25 to confirm it.
Andrea Leadsom, the Brexiteer Commons' leader, said she supports the Prime Minister but suggested there is an opportunity before the special European Council meeting to get "the best possible deal for the UK".
But Raab told the Sunday Times: "If we cannot close this deal on reasonable terms we need to be very honest with the country that we will not be bribed and blackmailed or bullied and we will walk away.
"I think there is one thing that is missing and that is political will and resolve. I am not sure that message has ever landed."
Both May and Raab are due to take their arguments on to television screens on Sunday morning.
At the end of a long week for May which left her battered and bruised but still standing, she told her critics that their alternative plans for a Brexit deal would not solve the issue of the Ireland border and the backstop arrangement.
She told the Daily Mail: "People say 'if you could only just do something slightly different, have a Norway model or a Canada model, this backstop issue would go away'. It would not. That issue is still going to be there.
"Some politicians get so embroiled in the intricacies of their argument they forget it is not about this theory or that theory, or does it make me look good."
Last week saw the departure of Raab and work and pensions secretary Esther McVey, plus the launch of a high-profile insurrection on the backbenches to remove Mrs May from office.
She responded by bringing former home secretary Amber Rudd, who quit over the Windrush scandal, back into Cabinet to replace McVey.
Steve Barclay took over as Brexit Secretary but with a reduced role.
Meanwhile Zac Goldsmith, the Richmond MP and failed Tory London mayoral candidate in 2016, revealed he has joined those who have sent a letter of no confidence in Mrs May to Sir Graham Brady, chairman of the 1922 committee of backbench MPs.
Writing in the Sunday Telegraph, Goldsmith said that under the PM's plan "in effect, Britain would remain in the EU, but without having any say".
He added: "Had that been the choice, I personally would have voted to Remain.
"The withdrawal agreement we have been presented with is unacceptable to Leave and Remain voters alike.
"It has close to zero chance of making it through Parliament and with only five months remaining, we cannot afford to waste any more time on it."
In a sign the Tory civil war over Brexit is not calming, Middle East minister Alistair Burt warned rebels the "consensus" that pro-EU MPs should reluctantly respect the 2016 referendum result could break down if she is toppled.
Burt, whose role spans the Foreign Office and Department for International Development, attacked a tweet by Steve Baker, deputy chairman of the European Research Group, in which the latter promoted a lawyer's legal case against the agreement reached with Brussels.
Burt wrote: "Be very clear. If an agreed deal on leaving between the Govt and the EU is voted down by purist Brexiteers, do not be surprised if consensus on accepting the result of the referendum by Remain voting MPs breaks down.
"Parliament will not support no deal."
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