I like the Fastex Buckles that are made to go on webbing .. that let you tighten both ends ..
you don't have to sew them on.
I don't like the look of how much they press into my sleeping bag and thermarest when I crank them down
use more than one .. get a stuff sack to put everything in that goes on the rack top..
side opening duffles like Ortliebs rack packs are great.
river dry bags are fine they load from the end..
I used 5 straps .. 2 run across 3 run fore to aft.. so nothing moves to affect handling either ..