Hoover Dam's old road is blocked off on the AZ side, so you can't drive from AZ directly to NV across the dam, you have to take the bypass bridge. Dam access is from the NV side only, and you have to drive 2-3 miles past the dam, then take the access road back.You'll have to go through the vehicle security check point to get to the dam, and I'm not sure what they would say with a boat/trailer, might turn you back, maybe not. There isn't much double vehicle parking by the dam, couple of spots at the bridge walking path parking lot, and "maybe" at the parking garage right at the dam if they allow trailers. Worst case, drop your trailer at the Hacienda's east parking lot, and then go visit the dam. Google map it and you'll see.
If coming from AZ, my first choice would be Temple Bar on the east end of the lake, next would be Hemenway and then Lake Mead Marina, both on the south end of the lake. T Bar and Hemenway have marina's with fuel and such, Lake Mead Marina is just a ramp now. There is also South Cove on the extreme east end of the lake, but it's just a ramp, out in the middle of no-where, with no services, and I wouldn't launch there unless you want to get away from everything (like I do).
Hemenway, Lake Mead Marina and the Vegas basin of the lake can be like a zoo during the summer, while T Bar is has less traffic. Of course, you will need to check LMNRA's website before you head out to make sure the place you are going to is open. Low water could close a ramp or a flood could wipe out a road, etc....
Have fun out there!
