I wouldn't worry about the substrate sticking to it, as long as your snake is properly hydrated and kept warm, it will easily pass whatever it swallows.
You should always wait a week after getting a new snake before offering any food, it likely refused because it was still stressed from the move.
At 5 years old, your boa only needs to eat every 3-6 weeks. 4 weeks being the best, 3 weeks being the absolute most often, and 6 weeks as the least often.
You need a hot spot of 88-90F and ambients no lower than 80F if possible, and no lower than 75F at the absolute coldest. Humidity should be 70-80%.
The only advice for raising humidity I can give you is ditching the tank and getting a modified tub or PVC. What you can do for now is cover 2/3 of the top with aluminum foil or cling wrap.
Here's a video of how I maintain humidity in my enclosures, I would advise doing the same since you're using EcoEarth. It will be much easier on you.
https://www.youtube.com/watch?featur...&v=1O-JNnS6XfM
Make sure the bedding falls freely from your hands as demonstrated, and no water strains out. Doing this, I only have to do this maybe once every 1-2 weeks and I can easily keep it 70-80%. You may not have such luck with your tank, but blocking off as much airflow as you can may help.
For the temps, what is your room temp? You may have to heat the entire room to bring the temperature up, it's unusual that two heat lamps can't bring it above 75F. Are you using a digital thermometer, and where are you placing it?
There's no need to treat the water at all unless it's unsuitable for consumption, in which case you wouldn't be drinking it either.
You only got the snake 2 days ago and it hasn't eaten, you shouldn't be handling the snake whatsoever. Give it 7 days, offer food, and then wait until it takes 2-3 consecutive meals without hesitation before you begin handling it. Snakes stress easily, and your boa has already refused food, I'd back off it for the time being.
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