Sorry I cant help with the ramp question...However, If you are unfamiliar with that area of the lake be careful, lots of hazards. It is well marked just be aware.
the Melvin Ramp is open to the public but parking requires a town sticker and is tightly patrolled from what I hear. 19 Mile Bay is only a few miles away and a great launch but parking is good walk up the road. I deal with this by bringing a bike...I drop the boat, go up to the parking lot and drop truck and trailer then bike down to the ramp and lock my bike to a telephone pole. Alternatively, the Lees Mills ramp is free and parking is good but it's a LONG ride back to Melvin through some tricky water.
Coming off the Melvin ramp, you have to stay between the channel markers but once you are out there are no problems. 19 mile has no hazard problems if you stay away from the Graveyard and should have good white perch fishing.