FREMANTLE ran out of fit bodies and petrol tickets in a deflating preliminary final loss to Carlton, but coach Trent Cooper has hailed the club's step forward in season three of the NAB AFL Women's competition.

The Dockers' next challenge is to build on their maiden finals appearance, starting with the retention of key players in a squad that could be raided by crosstown rival West Coast entering the competition in 2020.

AFLW Match Highlights : Carlton v Fremantle The Blues and the Dockers clash in the preliminary finals Share via Facebook

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Cooper was proud of his banged-up players after they fought through a fierce Conference A to finish second with a 6-1 record.

But the physical and mental toll of playing three must-win games to close the season – plus having to east travel to face Carlton despite winning more two more matches than the Blues – eventually told.

Inspirational skipper Kara Donnellan couldn't get up for the final after battling knee soreness all year, while star midfielders Dana Hooker (chest/quad) and Kiara Bowers (hip) headlined a host of players struggling before the six-goal defeat.

"I don't think we had much left," Cooper told womens.afl.

"Just the physical effort but also the mental effort getting up knowing it was a final every week…that probably told against us.

"On the weekend, the kilometres run were well down on where we've been all year."

Cooper's first season in charge at Fremantle was a major positive, and the Dockers ranked second for scoring after implementing a quick and direct playing style.

"We started the year with not a lot of respect from outside and probably not enough trust inside as well," he said.

"The group has got great trust in each other now and respect from other clubs, the media and the general public.

"Now we have to build on that."

Player retention and recruiting will be pivotal, with the competition expanding by four teams next season and the Eagles – or other rivals – able to poach up to eight players from the Dockers.

The sign and trade period runs from April 8-18.

"We wanted to create an environment here that was enjoyable, supportive and successful, and that's, we think, going to be the most important thing in retaining players," Cooper said.

"With the salary caps and the way the (player marketing agreements) work, West Coast is going to be able to offer players more than we can to a lot of our players.

"I'm not certain anybody's leaving yet.

"In discussions, they've all said how much they've enjoyed it, how much they love the club, how much they want to be here next year," he said.

"But they could leave for financial reasons."

Cooper, whose background was with the West Australian girls’ under-18s team and in female high performance, is concerned both Fremantle and West Coast might struggle in 2020 if talent is spread too thin.

"For both sides to be competitive we really need a lot of those good players coming back to the state (those who left as marquee signings in season one)," he said.

"If that doesn't happen and the talent is split, both sides would struggle next year you would imagine, on paper anyway.

"You'd need to get massive improvement from the local lists."

After seeing the challenges faced by AFLW players who work full-time, Cooper cautioned against the season being extended too long in 2020.

But he hoped for eight matches with three weeks of finals, including a wildcard system to avoid another potential uproar over uneven conferences.

"There's a lot of merit in the conference system, but they've got to get the right teams in them and make sure the conferences are even," Cooper said.

"I don't know what they do come finals. We obviously deserved to have that home final, I don't think anyone would argue that, Carlton included.

"It was a shame North Melbourne and Melbourne weren't there. They deserved to be there based on the way they played during the year, so I think wildcards have got a fair bit of merit."