When we bought our 1950 cottage overlooking the Pacific Ocean on the Oregon Coast, it was headed to foreclosure and had been vacant for quite some time. It had been left in heated for much of the winter to the point where the hardwood flooring was starting to warp, and both the main floor and the basement/garage smelled damp and musty. Although there was no black mold to be found, there was mildew in some dark corners.
And, of course, anything metal that is not stainless steel or similarly protected will rust very quickly at the coast.
I installed a programmable thermostat and set it to keep the heat at least at 62 degrees at all times. That took care of the dampness and smell in the main living area, and even the flooring flattened back out.
After insulating, adding a vapor barrier and sealing off the crawl space from the basement/garage area and installing new garage doors that were designed for use in coastal conditions, I was ready to tackle the basement humidity.
I bought a portable dehumidifier from Ace Hardware. It filled its reservoir in less than a day. Since we are not there all the time, I needed a way to have the water drain out. The laundry facilities, such as they were, were in an alcove in the garage. I bought an old microwave cart from a local Thrift store and set the dehumidifier up on it to drain into the laundry tub. Later when we turned the area into a second bath and laundry, I had a dedicated drain for the dehumidifier put in just outside the new bath/laundry.
The dehumidifier now sits on the floor just outside the bath/laundry and empties into the drainpipe shown sticking up by the new wall in the pictures. I cut the pipe down to near floor level, and only a couple of inches of the collar now show above the floor.
The basement/garage and laundry now remain at 50% humidity (unless I have the garage doors open for a while) and dry and free of smells and mildew. No sign or rust found on the garage doors, my tools, the car that is kept there or anything else that we store in there.
PS: The wet floor in the last picture is from cleaning up after cutting and setting tile in the new shower, not from any leak or trouble with the drain or the dehumidifier. :-)