Trader shop stock is individually instanced to each player and the filters are supposed to have a good-great chance to be in stock every 3 day reset iirc. Depending on how rapidly they accrue the dukes, shouldn't be an issue for a questing/looting focused group (which is where TFP wants us to focus right now), at max officially supported server size (8 players) a group could end up with 56 collectors chugging along on day 21 or 22 just from trader stock. Fuel-less horde summoning activated by simply harvesting the "workstation" with the check trigger ticking over a little bit less than every 5 minutes real time. If they don't want to deal with the hordes, leave the area for about an hour real time and comeback to the hordes despawned and the collectors turned off due to being full..
Edit: Seriously, the dew collectors have more in common with farm plots (place down, poke a bit after a set and unchanging bit of time, then walk away and come back later to repeat) than they do with workbenches and forges.