Whenever the contents are soft and the space is irregular — bedding, clothing, tent walls, and straps travel better in bags that conform and compress. Soft bags are lighter, quieter, and disappear when empty, which hard cases never do. Cases still win for crushable gear, dense stacking, and real impact protection, so most rigs end up running both, sorted by job.

The good ones are, and it matters more than people expect — fine dust works through ordinary zippers and coats everything inside. Look for roll-top closures, storm flaps over zippers, or tightly woven coated fabrics, and check the specific listing since construction varies across the collection. If the bag rides outside the cab, treat dust protection as mandatory rather than a bonus.

The size you can carry loaded with one hand — that's the honest ceiling. Oversized bags invite overpacking, turn into shapeless blobs that won't tie down cleanly, and become two-person lifts at exactly the wrong moment. Several medium bags sorted by job beat one giant one every time, and they let you leave a bag home when the trip doesn't need it.

Heavy and dense stays low and forward, soft bags ride high and fill gaps, and everything gets a lash point or a snug neighbor — a loose bag becomes a projectile in a hard stop. Use soft bags as padding between hard cases and body panels to kill rattles. Pack so the first things you need at camp load last and sit on top.

Only if they're built for it, and even then treat rooftop life as hard duty: constant UV, wind flogging, rain from every angle, and the occasional branch strike. Check each bag's listing for weather resistance before committing it topside, strap through proper lash points rather than around the body of the bag, and keep anything moisture-sensitive inside the cab regardless of what the fabric promises.