Trailers with dual axles or more are actually better in the sand than a single.. Give it a go with street pressure, but if it starts digging a trench with the tires, air them down. The trenched effect is harder on the tow vehicle to overcome, than the lower pressured trailer tire's rolling resistance.
BTW - For the truck, I never go by a specific PSI to air down to. The weight on each tire can vary depending on the load at that given time. And this load can make a given pressure seem either useless, or overkill.
Here is how I go about airing down for soft sand.
While still on hard pack soil or pavement, measure the distance that the rim is from the ground (a rough measurement within an inch is fine). Now, remove air from that tire until you have decreased this measurement by 25%. Example... your rim sits roughly 6" above the ground. Lower the pressure until it is 4.5" above the ground. This will increase that tire's foot print by 200%. This will get all tires to the correct deflation without going too far, or not far enough.
Note: Low profile tires don't follow the same rules as your standard light truck tires do. The rule for those is "Stay on hard pack, or bring a recovery strap with ya". :coffeedrink: