If it's any help, here's an idea I got somewhere off Youtube. It works well for me.
1. I got my wife to make me a cloth "cylinder", closed at one end, elasticated at the other (it's actually the sleeve off an old T shirt). It sits over the paper filter that is built into the shop vac (it's a Kaercher in my case).
Pic 1 - Inside the shop vac WITH paper bag
Pic 2 - The built-in filter cartridge PLUS old T shirt cover
2. When I'm doing something "out of the ordinary" (like picking up garden debris from the terrace - the garden vac we have is useless) I remove the paper bag as shown in Pic 1, and run the debris straight into the vac with the built in filter "protected" only by my old T shirt sleeve.
3. Otherwise, with "normal" shop debris I run the shop vac with both the paper bag AND the old T shirt/built in filter as a combo.
The only need is to clean the old T shirt every time I empty the shop vac. (I just bang it onto the edge of the garden dustbin. That clears most of the clag). Plus, "once in a blue moon", I wash the T shirt sleeve.
Along with not waiting until the paper bag is more than about half full (I agree with the previous poster about not waiting until it's really full) the old T shirt "filter cover" does seem to help prolong paper bag life.
So does using my cyclone, but I'm not yet using the cyclone regularly - that has to wait until I've made the cart to carry both the shop vac and the cyclone with it's own container.
I'm not sure, but expect to keep using the old T shirt filter cover after the cyclone is installed on the (yet to be made) cart. Though of course, the whole point of the cyclone is that most of the debris doesn't get into the shop vac itself, it goes into the cyclone's container.
Anyway, HTH