James Cummings will rely on Tommy Berry to demonstrate his navigation skills again with Doncaster Mile favourite Hallowed Crown to start from the second outside barrier.

Berry steered Vancouver to victory in the Golden Slipper from gate 16 of 16 and will have his work cut out on Hallowed Crown who drew 23 of 24 for Saturday's $3 million Doncaster at Randwick.

A full field of 20 plus four emergencies was declared on Tuesday with the Bart and James Cummings-trained Hallowed Crown to come in three places if the reserves miss out.

"Tommy Berry navigated very well in the Slipper and I hope he is ready to do it again," James Cummings said.

"It's lucky we've got one of the fittest horses at Randwick because he will have to do a bit of work.

"And if it's wet, that's another variable."

Hallowed Crown has a perfect winning record from three starts on rain-affected ground including the Group One Golden Rose.

Randwick received 10mm on Monday with the predicted Tuesday showers turning into steady rain throughout the morning.

That's not such good news for Paul Beshara, the trainer of South Australian horse Happy Trails who is lining up in the Doncaster for the third time.

"He's run in it twice and and it's been wet both times," Beshara said.

"I would prefer it to be firmer for him but there's nothing we can do."

In better news for Beshara, Happy Trails, a last-start third in the Australian Cup, drew barrier two after starting from 11 in 2013 and 17 a year earlier.

The Chris Waller-trained Sacred Falls, the 58kg Doncaster topweight, will have to contend with a wide barrier in his attempt to win the race for a third consecutive year.

Waller had little luck in the draw with Sacred Falls drawing 20, last year's runner-up Royal Descent 18, Moriarty 11 and second emergency Kermadec 19.

The Australian Turf Club directors opted not to use their discretion to promote Kermadec into the field.

Despite the uncertainty over a start and the barrier, Kermadec remains the TAB's second favourite at $6 behind Hallowed Crown at $4.60.