Hi,
Actually, there are many Outdoor projectors.
In all honesty though, your never going to reproduce the same clear bright image on an outdoor projection for less than £25,000 or more.
I've been an AV engineer for many years and we have tried many times to combat this problem within an acceptable budget to no avail.
The only way you can use projection outdoors in daylight is to create a back projection system with covers to blackout the light both between the screen and projector plus create a shadow on the front of the screen. This would probably take up as much space and weight as any Plasma or LCD.
The benefits to this are the size of the screen is at least doubled.
Using blackout materials, you can get away with using low powered projectors from 2500 ansi lumens upwards but, on the sunniest days, if your screen is static, as the sun moves, so does the shadow. This will then affect your screen. (eg: at 12 mid day, your image is good, at 4pm, your image is faded. Move the screen or create a larger front hood to overcome).
However, you can have plasma/LCD screens on wheeled systems which envelope into flight cases for Transit. The average size of the case for a 42" Plasma is around 6ft wide, 4ft deep and 5-7ft high (depending on lift system).
These are specially made to order.
Hope this helps?
Kind Regards
Nik