I'm planning on doing a similar thing (except a lot longer than 3 weeks.) what I'm going to do is
1) make an announcement so that my patrons know.
2) upload pages AS SOON AS THEIR FINISHED, so that they still sorta have an incentive to patron even while I'm on hiatus.
3) provide frequent news updates so everyone knows that I'm on track/not on track.
for what it's worth, (and you're one of my patrons so maybe you can provide feedback on this but...) 3 weeks isn't that bad of a hiatus? My comic is looking to go on break for like, 3-5 months, but then again it's not like I'll be 100% dead silent either, cuz I plan on uploading some minicomics in the middle of that.
Personally I wouldn't feel ripped off for a 3 week break, as long as the creator was really clear about what was going on, and if they needed a longer break that they came back and gave an update on what was happening.