An update:

I AM FINISHED WITH THE BACKGROUND. Thank goodness!! I think I've probably spent 18+ hours on it at this point. It was about a 12 hour project at the point when the foam started melting. Then I had to do 3 coats of polyurethane, at 1.5-2 hours per coat that's 18 hours. And that doesn't include the several hours I've spent running around to stores getting everything needed for it. So I'd say this is a 20 hour project. I think it came out nice, though - just a little bit too shiny for me, but not horribly. The polyurethane was satin, not matte, so that's why. I think it will have a nice wet-looking shine to it when it's in the vivarium. I still have a little work to do on it...but nothing that's going to be painstakingly boring like applying polyurethane for hours on end was. It is drying in the garage right now with a fan on it to get rid of the polyurethane smell. All that's left to do...put it in the tank, then hot glue it together with my low-temp hot glue gun. Note to self: Test on a spare piece of foam, first!! Then after I have my substrate in, with the background hot glued into one big piece, I can add moss to it.

I went to Petsmart today looking for a humidity gauge(hygrometer) and walked away empty handed...so I went to Petco, which was right down the street, and found one for $6. It had good reviews on Amazon(4 out of 5 stars) so we'll see how well it works. If it doesn't seem to be working right I will order a higher rated one from Amazon. However I am looking on Amazon right now and it seems all the highest rated humidity gauges average 3.5-4 stars so maybe the one I got is as good as it gets. We'll see! I should pick up a second one to compare them against each other.

I bought a 1 gallon sprayer for misting down the vivarium until I can afford an automatic misting system.

I need more charcoal to make my ABG substitute...Orchard Supply Hardware had 2 bags, I needed 5. Thankfully they're getting in more tomorrow or the day after.

I found Sheet Moss!! They had it at Petco, believe it or not. It's in a baggie on my couch right now with all of my other stuff for this project. Now I have to decide what I'm going to do with it... It was only $5 so I thought I'd buy it. It's a small portion, a bit bigger than my hand, but it's probably cheaper than paying shipping from ordering online. I'm not sure if I'm going to attach it to the background, wood, or just let it rest on the substrate...

I found some awesome Oak branches. Oak is safe to use in a vivarium, if I remember right? But...how would I sanitize pieces that are 3-4+ feet long?? I can't boil or bake them, obviously, they're too big.