As a youth I mowed lawns for a living. My dad built a simple ramp out of 1x6 I think it was just as you explained. That allowed us scrawny kids to push the mower up into the truck. Not sure how heavy you shack is but I would guess 2x4 would be plenty heavy enough, are you thinking 2 2x6 or just one. The one my dad built was 2 ramp pieces with two cross pieces to hold them together and at the right spacing. I use a 2x6 short (3') ramp to get my old skidoo on the trailer. A 2x4 holds the 2x6's together and is just a couple inches from the end of the 2x6, this creates a "notch" to rest on the trailer so the ramp can't push forward.
