So I had to head to Wally world to get a ball mount to tow a small boat today (on a whim) and I've got a 3.5" RE lift with a jillion pounds front and rear for Smitty bumpers. I picked a 5" drop ball mount. Looks sufficient. Any for sure mounts that work?

 

Lift heights vary. Tire heights vary. Trailer heights vary. Trailer tire heights vary.

You need some type of adjustable hitch setup if you are looking for "for sure mounts that work?" Just back the jeep up the trailer and measure?

 

Normally 19 inches from the ground to the top of the ball for most trailers. That will get you in the ball park . Go to u haul they have a variety of sizes you can try first to get the right drop.

 

Put a RK 2.5" lift in my JK. Ended up with 3.5" in rear (no back seat)
With 35's, I use a 6" drop and my Jetski levels out perfect in the rear.

 

I have a 2.5" lift and 35s, & use a 5 1/4 drop which levels out my trailer perfect. +1 either measure or get an adjustable.

 

It's really not about the size of the lift when it comes to figuring out the drop, it's more simple math. Park your tow vehicle on level ground then measure from the middle of your square receiver to the ground. Then level the trailer that you will be towing and measure from the bottom of the tongue where the ball slips in. Subtract these two measurements and that is how much drop you need.