Its not that bad. You register the tube. Then you can switch out end caps and baffle stacks.
If you google "solvent trap" you will find many many sources.
I frankly think this whole solvent trap is of dubious legality. But the risk is to the seller of these traps. If you buy it then immediately Form 1 it (and pay the tax) and engrave it, then you are 100% squeaky clean. Legally speaking you have made a solvent trap into a silencer. So you are good.
These DIY cans are also useful for testing muzzle threading and ammunition because if you have a baffle strike, you just replace the baffles and maybe the end cap with the exit aperture and you are good to go.
I know that in my testing of very heavy, very slow .300 blackout loads out of my 8" SBR, its dubious whether it will stabilize adequately to be used in a can. A home made $150+stamp can provides a low risk way to test things for someone who likes to tinker.
The other advantage is that once you pay for the stamp on an adapter, you can build a can for every application whether it is one of the solvent trap, flashlight, or oil can.