...on the D'Kora, Jem'Hadar, Temporal Destroyer and other lockbox ships?

You don't. However, there is a console that allows you to place your trophy if you are KDF for a specific mission. The trophy will be placed on your ship, but you can't see it.

One of my fleetmates has a ferengi toon. He took the time and effort to get the big gold pressed latinum floor trophy playing dabo. Then he anted up for the dkora. He was frustrated, to say the least, that he couldn't place his GPL trophy on his dkora.

It makes no sense that you dish out the cash for a lockbox ship, and there is no interior to speak of.

I'd really like to see one deck added to each... and if that means writing missions that include these ship interiors to justify the work, go for it. It'd be great for the Foundry too.

Just one deck with a rec room, trophy area, office, quarters, and transporter room for each lockbox ship.

This irked me as well about my D'Kora. The funny thing is, if you look at the aft room, there are panels on the wall. It's almost as though they were thinking about allowing wall trophies and never turned it on. There would also be room for a latinum pile floor trophy next to the trader.

Another improvement would be to get rid of the Cardassian type console next to trader and replace it with something similar to the Exchange terminals you see in ESD and DS9. Have the trader standing in front of it and entering data into his PADD, pondering the info on the terminal and etc. A lot of real life traders spend their time in front of a monitor.

It is in some ways disappointing to not have trophy mounts on my D'kora. There is however the pure joy of having all doff contacts in such a small area (the trader is the only one that's not right at the helm). I wouldn't want to lose that if they expand the interior.