Hi!

We've cleaned underneath, vacuumed out the drip pan, removed all the
food, but there's this smell that's particularly prevalent when you open
the door. We've put baking soda in, but we just can't seem to get rid
of it.

There's still a lot to look at here. Most modern refrigerators have a sort
of plumbing system that channels water (generated by the defrost cycle) away
and to a structure that allows it to evaporate.

Unplug the power (don't just turn the fridge off) before trying any of
these.

There might be some area where the drain has become plugged and is not
letting water get away. Given enough hot/cold cycles, it could really turn
nasty and stinky. If you can get at the lines and channels that are supposed
to take this water away, pour boiling (or at least very hot) water down
them. This can flush out a clog in the lines. Be careful, however, as this
could cause parts to melt or swell.

Also look in the fan ducting. Maybe something got spilled or leaked into
that area.

Smells can also hide underneath the plastic "skin", as it isn't always a
solid piece. Sometimes it happens that something gets spilled and leaks down
underneath the points where the plastic comes together. I've never had to
deal with this kind of a problem, but I have seen it happen and I don't
think it would be fun to fix it.

William