The duallies generally are worse off than the SRW's. Not that you shouldn't bring one out there, because plenty of people do. Just depends on what the sand conditions are and what you're pulling. Sometimes everything is getting stuck no matter what and sometimes 2WD cars are driving all over the place.
I can't lock mine up. But a better test would be to get into some loose dirt and pull the trailer from a stop with only the trailer brakes fully activated. If the trailer wheels turn and don't skid in the dirt you've got brake issues.
Pull your drums and check the internals out as well. My axles seals blew once and leaked grease all over. I couldn't get my wheels to lock in the sand.
Not sure if I should have posted this in the class A section but I'm thinking there will be more experience in this forum.
I have a friend bringing his class A out to the dunes to camp with me. I've been going there for the last ten years with my fifth wheel, so I know about airing down and coming in at low tide. Is there anything else that's going to help out my buddy when he bring his motorhome out there? One issue I already see is his front valance is so low, I don't think there is any place I can hook up the tow strap to if he needs a tug.