Sounds like it will work. I'm more worried for the TV outside, with possible condensation, and just the outdoor elements/temperature in general, but OTOH I wouldn't be surprised if it lasted for a while out there. Just try to take care of it out there I guess, perhaps with some cover during non-use.
You can use search functions in the TV subforum, or just ask me, and I can link/post/pm some recommended SM offsets. YMMV due to unit to unit variation, etc, but most if not all people who do them are pretty pleased.
Lastly, you might consider waiting for the 2010 models to roll out, if only due to the videophile complaints about '09 Pana plasma rising in black level. AFAIK, this is caused by voltage increases, by design, to counteract phosphor wear, but they seem to work poorly/prematurely according to some cases. I am sure Pana might keep this stuff close to the chest, and perhaps it only happens with models from earlier production runs, who knows. REALLY THOUGH, if for 30 min a night, I wonder if you guys would notice if you even had one of the problematic sets.
If you need it now, want a 50", want a plasma, then go for it.