I'd tie it down using both side rails and cross rails if feasible. 1500 miles is a pretty good drive. If not, crossbars for sure. Use pool noodles on crossbars maybe to dampen vibration. Be careful with auto hatch door opening. Use red flag if needed fore/aft as required (by law...I don't remember requirements...3 feet extended from car probably)

(not my car, picked from internet)

 

I appreciate the noodle idea. This is not my car but the same crossbar and rails set up. I was going to wrap the strap through the side rails bc I thought it would be more secure, but I really appreciate your crossbar advice.

 

Ditto on both the rails and the crossbars. Multiple straps as well. Safe travels!

 

I carry a 16 foot sea kayak quite often. Ratchet strap it to the crossbars, two per bar because redundancy is good. It wouldn't hurt to use ropes on both ends to hooks on the bottom of the bumpers. The "bow and stern" ropes don't need to be very tight, but they prevent wobble from working the ratchet straps loose.

 

Stop and check the tie downs after you drive a few miles. They will usually need to be tightened down after the load and straps "settle in".

 

Or maybe buy a new ladder when you get to your destination? BTW, Years ago, I used to deliver long sail boat masts on top of a pickup truck rack, from southern Ct to mid coastal Maine/ Just had a flash back of driving on 495 around Boston and remember, people not seeing the red flags on the masts.

 

this is going to feel really huge when you put it on the car, but for perspective, at 15ft long the outback is longer than the ladder.

i second and third everything. pads of some kind, ratchet straps, and check it after a few miles. oh and drive slowly, as the wind against it picks up force with the square of speed. not super slow. reasonable. pretend you're a painter, not the meth addled ones who drive 80, the ones you actually want to hire who enjoy prep work.

 

Pretty good chance the open ends of the steps will resonate and moan in the wind!

 

Pretty good chance all the rungs will make a **** load of noise also....