As i have no storage chests and i spent my crowns on a merchant and a deconstructor i see that there are no chests for me to purchase with seals or trade bars, which i now have an abundance of.
You can get chests for writ vouchers, tel var, and maybe alliance points. I might be misremembering the AP, though.
Certainly no reason to spend crowns on them.
Seals (formerly seals of endeavour) have only ever been used to buy crate items, not stuff sold directly in the crown store. It's something put in place to comply with Microsoft's policy that anything in loot boxes has to be earnable by playing.
Trade bars as far as I know are used for old bonus items and possibly some new unique rewards, but also can't be used to get anything currently in the crown store.
That means it's not surprising neither can be used to buy storage chests. As other people have said there are options besides spending crowns on them. Writ vouchers are probably the easiest option for anyone who does crafting, and for anyone else tel var is the way to go.
PC EU player | She/her/hers | PAWS (Positively Against Wrip-off Stuff) - Say No to Crown Crates!
"Remember in this game we call life that no one said it's fair"