I checked slip availability last month at Prieto Marina in Mandeville off of Bayou Castine. I was told that there was quite a waiting list. Slips with floating docks were available in Madisonville at Marina Del Ray. Slips with fixed docks are also available in Oak Harbor in Slidell.
The Sail to Madisonville should take about 5 to 6 hours depending on conditions. Be sure to give Goose Point a very wide safety margin. Also, be sure to notifiy the causeway bridge tender 3-4 hours notification by phone or VHF. The entrance to the river in Madisonville is well marked. I also think it is a good idea to check with the locals at Marina del Ray for water depths and clearance. Finally, watch out for those afternoon thunderstorms; they can be nasty & the lake can build up a real chop with winds associated with the storms. Have fun!!