I've flown out of Dulles twice 1-12 day trip and 1-28 day trip. My third trip out of Dulles is in 63 days, on a 43 day RSA trip.
First trip: I used the open long term parking area. I didn’t feel comfortable in a security sense, and leaving my vehicle out in the open, in late May early June, DC weather.
Second trip: I used the parking garage. Traveling to Zimbabwe and RSA mid May through mid June. I felt better having my vehicle sheltered from the DC weather and a tad bit more security comfort.
As for this upcoming trip: departing Dulles on 27 April and returning 09 June. I haven't decided on which alternative to go with: A or B. I'm leaning more towards B.
A. Long term parking for 43 days in airport garage parking. The Pro: having my vehicle handy to head home or to rest up at a nearby hotel after return arrival. The Con: the costs of 43 days of long term garage parking.
B. Rental car. Round trip car rental fees would be slightly more or less than long term parking fees. The peace of mind not worrying about my vehicle being vandalized or stolen while I'm gone would be a big mental relief.
C. As previously mentioned; However, not an option for me on this trip is staying at a hotel prior to, and possibly on return, that offers long term parking in a designated parking area of their or a nearby parking lot.
This Option C can become very unnecessarily expensive, very quickly, and at the most inopportune time, up on return arrival to the US. And there is little to no guarantee about the security of one's vehicle from vandalism or theft.