Dave Fest location
Dave Fest is held on a beach called "M'pai Bay" on the Northern part of the Koh Rong Sanloem Island, you cannot access Mpai Bay on land (neither on foot or by car) from other parts of the island and boat taxis are not common at night, so recommend to book to stay on M'pai Bay to enjoy the festival.
Transport
You will need to get a boat from Sihanoukville Autonomous Port here: https://maps.app.goo.gl/fw34QijTX2fpaDBx5
Ferries run several times per day leaving Sihanoukville at 8AM, 11AM, 2PM and 4PM with GTVC and 2:30PM and 5PM with Buva Sea, if you are travelling from Phnom Penh, allow four hours for the journey, so for example if you wish to get the 11AM ferry, get a 7AM bus.
Ferries leave M'pai bay to Sihanoukville 6 times daily at 8:35AM, 11:45AM, 2:45PM and 4:45PM with GTVC. Buva Sea has ferries at 6:30AM and 3:30PM
Accommodation
M'pai bay has a range of places to stay at ranging from $10 per room per night to $200+. Remember you should aim to get accommodation on M'pai Bay and not another part of Koh Rong Sanloem if you wish to access events easily.