In a remote control project, I have a small FM 433.92 MHz sender
module which according to its specifications requires a "30-35 cm whip
antenna for 200 meter range in open air". However, I'd like to put the
antenna INSIDE a plastic box, containing some electronics, which is
only 5 times 10 times 20 cm, where 5 cm is the height.

I wonder how should I proceed to maximize the range of the
transmission (of digital signals from the box):

- Should I squeeze in an antenna horisontally in the box?
or should I utilize the vertical space available?

- Should the antenna be as long as possible, or a harmonic division of
the ideal "30-35 cm"?

- Also, what material should the antenna be made of? And what shape
(thin/thick, tube/square, solid/hollow)?

- Can I use a loop antenna?

Basically, I have no restrictions on the recieving antenna, other than
distance. How could I design/position it in order to maximize the
working range from the transmitter?

(I hope this question is not malplaced in this forum. Any thought on
any point above is most welcome!)