canndo, hey first thanks for this thread. This is good stuff. I am rooting for you.
Second, looks you are fighting some environmental and contamination difficulties and I had a suggestion or three for you.
Have you ever thought about making yourself a DIY incubator? Kludge a $50 craigslist freezer [I think freezers are preferred more than refrigerators for this type of use (cycle duration/frequency maybe?)] with a digital thermostat ($60) and then add in some lights...
**poof**mad scientististy incubator**poof**
I know you're trying to stay away from buying all sort of expensive lab kit, but this sounds like a simple cheap and effective solution. This type of incubator is used by some homebrew, cheese and mushroom folks. I like this option if you have a room that isn't air conditioned and it's too much to add AC just for your PTC.
also, I know you said that you aren't going to buy a glove box or a flow hood, but what about a simple cheap DIY glove box? You could fairly easy build yourself one from a 20gal aquarium($5 yardsale), some lexan ($20) and some glove box sleeves...
...I know glove box sleeves are expensive, but I've seen some for $100...
"Still Too Expensive!!!" you declare!?!?!?... You could make yourself pair of DIY neoprene iris(es) arm seals for next to nothing.
If you're totally against a DIY solution you could go the super simple rubbermaid box route. I have noted several sources recommending a simple plastic bin as a makeshift hood in lieu a glove box or flow hood.
Keep up the good work.