Pseudo Glasshouse... advice appreciated

[OzPhal]

Hi everybody,

I live in Southern Australia and grow Phalaenopsis spp. All of my plants at this stage are seedlings with leaf spans of around 100mm. I also have one deflasked P. lobbii. I plan on growing more flasks up in the future along with seedlings so I'm wanting to build a small 'mini' glasshouse. I'm planning on building a table - around 2m X 1m which will have heat cable installed under a bed of propagating sand and then covered in coarse gravel. The Phals will sit on the gravel. The sides and roof i'm planning on covering in with twinwall polycarbonate and then i'm going to incorporate some style of door at the front (maybe something that is hinged at the top and i can simply lift up). Internally i'm going to have temperature control, an air circulation system, and also install a small scale fogging system to control the humidity/temperature, I also want to set-up some sort of system so that if the temperature gets too high then vents in the top and at the bottom edges will open to allow some fresh air to flow through. My goal will be about 28oC and 80% RH and then i'll need to take in to consideration the intricacies of some Phal species... I may install lighting down the track if it's necessary. This unit will sit outside so obviously everything will need to be waterproof etc. I might consider moving it inside if I find that the costs associated with keeping it warm are too high. I'm wondering if anybody has any advice on:

1) Grade of twinwall polycarbonate to use
2) Suggestions for thermostats/humidity controllers
3) DIY high pressure fogging systems (1,000PSI units)
4) Suggested heating cable to use
5) Any pitfalls i may come across

Thanks for your time...