A horse on the verge of his own jumps racing accomplishment is considered the biggest danger to Bashboy claiming a record third-straight Grand National Steeplechase at Sandown on Sunday.

Trainer Patrick Payne will saddle up two runners in the five-horse field including Sea King who will attempt to become the first horse since Mosstrooper in 1930 to win the Grand National Hurdle and Grand National Steeplechase in the same year.

"Bashboy is going to be very hard to beat," Payne said.

"But I'm not conceding defeat to him with Sea King."

The Ciaron Maher-trained Bashboy has 74.5kg and is the $1.65 favourite ahead of Sea King, who has 69.5kg, at $2.60.

The other three runners are all at double-figure odds including the Payne-trained Australian Steeplechase winner Krase who is the outsider at $26.

Sea King has had to qualify for steeplechase racing in a trial since his Grand National Hurdle win less than two weeks ago.

Payne thought the time frame might have been going to be a bit tight to trial last Friday despite keeping Sea King ticking over in work, but then the trials were rescheduled until Monday because of rain.

"They called the trials off (last Friday) and rescheduled them for the Monday and we were working him on Friday and Saturday morning and he just seemed in fantastic order," Payne said.

"So I thought `let's see how he performs in the trial'. I thought he went really well so I thought it was silly not to run (on Sunday)."

With champion jumps rider Steven Pateman riding Bashboy, the mount on Sea King has gone to Richard Cully.

Cully's wins this season for Payne have included the Grand Annual Steeplechase on Chaparro and the Australian Steeplechase on Krase.

"He comes out and rides work for me and he's a very good rider," Payne said.

"He knows the horses which I think is very important for jumps racing."