Help with 433Mhz Antenna Location

In general, antennas should be kept away from other conductive structures that are not an intentional part of the antenna system. For example, a monopole antenna (e.g. whip) might be designed to be installed onto a metal structure that acts either as a counter poise or as a ground plane.

Dipoles (like your selected antenna) will provide a symmetrical cardioid radiation pattern if they're installed in free space, not affected by nearby conductors.

A metal surface approximately one quarter wavelength (about six inches ?) behind the dipole would act as a reflector increasing signal in the opposite direction.

Your box is more than big enought to possibly be arranged into a corner reflector with quite high gain in one direction. This depends on exactly what side is open.

Acrylic is not a bad dielectric as far as I know.

The best choice depends where you want the signal to go. If you're not sure, then mount it high and clear of other metal.

Your antenna is a dipole, very weak signals off the ends. Everything around it will affect your antenna pattern coverage. Which is not comforting.

You should specify what area you want to cover, such as Omni (in which case you chose the wrong antenna) or forward/aft/upwards. Then you can be guided.

If you need to look in a quadrant, you might want to switch to a patch antenna and place it on a metallized surface. Be careful buying one, I just found a Chinese 433 Mhz patch, said 433 Mhz patch antenna right under the picture, specs says operates at 450-470 Mhz ? damn puzzling.