I think fourchon pass might be too dangerous for a 18ft flat. To go soak crabs on the bottom for big reds like you want I would suggest launching at bridgeside marina and go in the pass between elmer's island and grand isle. That would be a safer spot to acheive your goal. Good luck. Start with 1/2 a mullet and if the sharks move in go with a whole crab. Sharks hate crabs (most of the time).
I don't think you'll have a problem. As long as you arent' using a mushroom shaped anchor. Any type of pointed anchor and you'll be fine. If it's really bad, you can put the boat on to the beach real easy and fish from there. If the current is bad, then the fishing will be good. But it's not crazy current in there (in my opinion). Remember to put out a good bit of rope so the anchor won't slip. The more you put out, the better it will dig. Bring a radio to pass the time. The fish are huge, but the bite can be slow. I usually throw some jigs while waiting. I put 2 or 3 large reels off the back of the boat with bottom rigs. (big rods)
Understand this, the current will be intense in any inlet (pass), however, the water disperses quicker coming thru Caminada without it being rocked on both sides...and there is no commercial boat traffic. And you're 2 minutes away from a safe harbor should the weather kick up. Best of lucky, and ARRIVE ALIVE!!!
How big is your boat? I've anchored in a 17' aluminum bass boat without any problems. It depends on the weather and the wind angle as to how big the rollers can be. The last few trips through the pass they haven't been bad at all. The trout have been on the beach the past couple of trips along with spanish mackerel, white trout, reds, and all sorts of other toothy rascals. Hope this helps.