Soft things like swags and tents are a lot safer than hard things like kayaks ... just strap it down a bit harder with rope, ratchet strap, tight occy straps ... whatever.
Ratchet Straps are the go - bit spend good money and get ones that won't have the plastic handles fall off.
Get the stuff on the roof, pack a bit more - tighten.
Drive for a bit - stop rest (revive / survive) - tighten.
Don't try to use all the tape / strap better to put a few extra on than zig-zag it back & forth from one side to the other the first few sections won't tighten, only the last.