The inside of the lid has all the fittings for securing the typewriter in place. This is unlikely a home-made case, but a professional job; factory-made.
Inside is the very common and unremarkable Remington Portable #2 typewriter.
It is in a bit of a state and misses a few parts, but these are very well-designed and resilient typewriters - it could fix-up quite well.
Another indication that this is a Remington factory-supplied variant is the case-tabs at the rear. The locking tabs for the case lid protrude through the angled back-panel of the typewriter.
The case tabs pass through slots in the typewriter's back-panel, it's a bit of a wiggle to remove the machine from its base.
This back-panel is a different part from the common, 'normal' back-panel of these 1920s Remingtons. The profile is different and of course there is an extra slot for the case tabs. This looks like a factory-made variant.
The case is made of aluminum, about 1.3mm thick. It's had some repairs, one of the cast corner-pieces has been replaced with an improvised part and overall it's got its share of 'dings'. It doesn't close properly, but still very sturdy and should bend back into shape.
The typewriter itself is very common (and in not-so-great shape), but this aluminum case is a variant not seen before. The uncommon case was the reason to go out and pick this machine up, it was local and very reasonably priced. (Otherwise, I have quite enough Remington Portable typewriters ;-)
Perhaps these aluminum cases were marketed for the tropics, although locally here is certainly not a tropical climate :)
First more cleaning and some research into this!