Bell made 115 and Trott spent almost six hours at the crease in his unbeaten 113 against a second-string WACA Chairman's XI.
But there was little else to cheer about for the visitors, who couldn't even land first-innings honours and were forced to settle for a draw against a WA line-up stripped bare of their best talent.
England's selectors hoped the three-day match would give them a clear indication of who should join James Anderson and Stuart Broad in England's three-man pace attack for the first Test against Australia in Brisbane, starting November 21.
They also needed one of Ben Stokes or Gary Ballance to fire as they try to fill the troublesome No.6 slot.
None of their hopes came to fruition, with Boyd Rankin, Steven Finn and Chris Tremlett struggling with the ball, before Stokes (4) and Ballance (0) failed with the bat.
The team's fielding also left a lot to be desired, with six catches going to ground.
England were cruising at 2-330 when Bell retired in order to give his teammates some time in the middle.
His departure sparked a collapse of 7-61 as England were bowled out for 391 in reply to the WA side's 5-451 declared.
Finn (2-53) and Rankin (2-34) found some form late in the piece, but it was too little, too late as the WACA side finished at 5-168 before the game was declared an early draw.
Queensland's Chris Lynn followed up his 104 with an unbeaten 61, while star WA all-rounder Mitch Marsh also performed strongly with quick-fire knocks of 58 and 62.
England are set to recall skipper Alastair Cook, batsman Kevin Pietersen, paceman Stuart Broad and spinner Graeme Swann for next week's four-day clash with Australia A in Hobart.
The visitors will have just one more warm-up game after that before settling on their Test XI.
Stand-in England skipper Matt Prior conceded the team didn't bowl well on the first day.
"But I think they improved through the three days and got through that bit of rustiness," Prior said.
"Steven Finn bowled a long spell there, and certainly the last four or five overs he was really hitting his straps again, hitting a great area, and his pace was up.
"Boyd Rankin I thought was fantastic all day.
"Tremlett got better and better and got more rhythm as the game went on and certainly as today went on."