Okay so I've prevaricated long enough that there's only one of the chokes available at Mouser and they're on backorder with an eight week lead time

. Maybe I'll go with 4x22kF caps to start and add the chokes afterwards if I feel I need them.
I think I'll draft a PCB to hold the bridge and caps. I can add Quasimodo style snubbing and a fuse. I'm intending to use these fast recovery diodes at 71p each:
https://www.vishay.com/docs/96201/vs-mur2020ct-m3.pdf
They're rated at 200V and 20A so will be hardly working at 20V and 2A. I don't think they should need a heatsink but before committing to having the PCB fabbed I wanted to run some numbers but I'm struggling a bit. Power in the diode is IV. PSUD reckons that for a 2A DC after the filter has a peak in the bridge of 5.2A AC. I don't think there is a root 2 type conversion for current as there is for voltage so I'm not sure what to use for the I value. 5.2A doesn't feel right, perhaps half is better???
The forward voltage drop Vf looks to be around 0.6V if I've read Fig 1 of the above datasheet correctly.
So Pd = 2.6 x 0.6 = 1.56W which doesn't feel like too much. But I can't see anywhere on the datasheet where the power rating of the diode without a heatsink is given.
Looking at a thermal calculation, Tj = Pd(Rjc + Rcs + Rsa) + Ta
Assuming Tj = 175C (max), Ta = 25C, Pd = 1.56, Rjc = 1.25C/W.
If no heatsink should Rcs = Rsa = 0? This can't be correct as the equation would suggest having no heatsink is better than having one!
But anyway, Tj = 1.56(1.25) + 25 = 26.95C << Tj max therefore okay without a heatsink.
Or am I just making it up?