Strategy/build suggestions for using an armor unit in TT?

What other units do you have? In the case of giving QR to your W! Chrom-I’d probably skip that unless you plan on giving distant counter to him as well.
If i was in your position, I’d probably build a team like this, winter chrom/ a nuker(so like bridal cordelia, reinhardt), a dancer, and another nuker- with this setup you basically only use the above 3 units(with winter chrom just there for 40% bonus).

If you have nowi(all ready with skills and all that)-her alone is incredibly good in this TT-add a dancer and some counters to red units and you are all good.

For your refinery question, def or atk is where i would refine winter chrom’s weapon just because speed won’t do much to avoid doubles or give him more doubles against more enemy units.

If you absolutely have to use the aforementioned units and just want to switch one or two units-I’d probably place a dedicated healer and a dancer to replace lancina and masked marth(like axura and genny)

There are definitely more options given the units you have like for this TT, I’m running two armors in W!Chrom with brave axe set, Winter Tharja(with additional Aether special) and repo, Nowi, fully buffed, lucina(for healing and rarely to kill units).

If you have a good Flier, I would recommend to use it along with the Guidance seal. Your Chrom is most likely dying because of bad positioning, and being able to move 3 cases away would do a lot to keep him alive.

I run a similar setup with W!Chrom, Bow Lyn, M!Marth and a blue dancer, and while they don't always make it through all 7 maps deathless, they are fairly consistent.

Skills & Seals:
My Chrom runs Bonfire as his special and otherwise just his normal kit. For his seal, I'd suggest Distant Def since many threats are ranged units or Panic Ploy to take advantage of his insane HP.

Keep in mind that Wary Fighter cancels out doubles naturally so he doesn't necessarily benefit from speed in terms of evading doubles. If you put QR on him, he'll be able to double, but be weak to doubles from fast units.

Consider upgrading his weapon with +Def to increase his tankiness.

Other options:

It's difficult to tell without knowing your roster, but especially for units like M!Robin a green tome nuke like Nino can be a useful addition.

If you have other options for team building, consider bringing 2 (ranged) nukes and a dancer so you can keep Chrom away from danger.

Another option is to consider bringing in a flier (with Guidance) or horse unit with Reposition to get Chrom out of danger after he attacks.

Hope this helps.

You have several movement skills available(guidance, armor march(if running multiple armor), reposition). If you are having trouble keeping him healthy there is sol, aether, noontime, renewal, or bring a healer. He has pretty good defense and should only be fighting blues and possible greens, so he shouldn't be getting damaged too hard.

I am currently running WLissa and just using reposition to move her if I need her to kill something. But I am also running Nowi(who is pretty unkillable in this TT, especially with the buffs).

Don't refine for spd, it is pretty much worthless on Chrom. You should go +def, or if you feel the need for the extra 2 atk then +Atk.