Improvements made to your primary residence do not result in a tax deduction when you incur the expense. You will not be able to write off the dehumidifier or the crawl space sealing this year.
However, you should hang on to the information so you have it available in the future should you ever sell the home. Those expenses can be added to your cost basis at the time of sale, which will help reduce any gains you have on the sale of your residence. If you are tech-savvy, a few minutes spent scanning and saving your invoices and receipts for the work, and saving it somewhere that you can retrieve in the future could save you some money down the road. If pen and paper are your thing, set up a folder for home improvements and stash all these kinds of receipts in it every year.