Best to use a .204 type seating die. I use a Hornady Custom Grade .204R seater that will work on any/all .204 calibers.
Brownell's has a .20 Hornady seater die, in stock, for $29.99 - look for Hornady dies/die sets for any/all .20 calibers.
Any Hornady seater of this type having the shorter body may be modified by replacing the inner sleeve and stem with those intended for a .204 diameter bullet
The custom Lee collet die with a seater die is a real good solution - I might get both.
The .20 Practical is just that, probably the best mid range, hi-volume, rodent killer cartridge ever. Buckets of cheap .223 brass, small powder charges, minimal heat & long barrel life, and relatively inexpensive bullets. I use either CFE223 or IMR8208 with the 40 gr. .204 VMax bullet & CCI #41 primers. My rifle has a 24", 11 twist, #3 McGowen barrel & weighs 7 pounds. The barrel is 8 years old & with about 3,500 rounds thru it. A Ruger M77 MKII that was a .223. I also use a .223, .204R & .22-250.
I had my .20P shooting yesterday with remaining 2020-21 season ammo, 25.5 gr. IMR8208 & 40 VMax. Impressive 300 yard performance during light variable winds. A good choice!!!