I use the
Moroso 89570. It's not cheap, but it's accurate.
Bruce
2010 Skyline Nomad 297 Bunk House, 33-1/4 feet long
2015 Silverado 3500HD LTZ 4x4, 6.0 liter long bed with 4.10 rear, 3885# payload
Reese Straight-Line 1200# WD with built-in sway control
DirecTV -- SWM Slimline dish on tripod, DVR and two H25 receivers