For your use case I would get the HD. I am not sure how sturdy the bed sides are though. After fiddling with it a bit the SE seems to be made much more sturdy than the bed itself is.
I went with SE instead of HD. I feel that the HD is for larger trucks so you can put wheelers up there or a tent.
I would be reluctant to put too much weight up top because it would mess with stability.
The HD is made of a thicker aluminum and comes with more cleats. Other than that it is the...
I picked up the front and back liners and really like them. Maybe they changed them. They fit well and don't move around. My feet don't slip on them so far. I will update if I notice any issues.
@sarcasm, wouldn't you just strap the wood to the thule rails? I am asking because I have been wanting to buy those very same rails for my truck to carry some light wood 8' 2x4 / 4x4 etc, edging etc.