I only use lenses in shutters, but I know a lot of people don't. Personally, I find the hat trick or a lens cap too risky given the effort required to get a ULF camera to where you want it to risk vibration caused by not having a shutter. Yes, a Packard is a solution too. At present, with the current availability of a fast film with great reciprocity charateristics like Tmax 400, I find that I am shooting a lot at around 1/2s which is a bit tricky without an accurate shutter. Also, it probably depends what process your negatives are destined for: If you print on Pt/Pd, you really do not want to have a negative which is a stop denser than you need (because you couldn't get an accurate exposure) - I loathe printing when exposure times get beyond 20 minutes - it really destroys my productivity and takes the fun right out of it.
You are right with the Kowa - 240mm. On some, the front element cannot be simply unscrewed and then put into a Copal 3S shutter - however, I can tell you first hand that SKGrimes can easily remount the front element from this type into a "Copal 3S" fitting mount for about $200. If you spend about $200 for a Kowa which cannot be unscrewed, you can still end up with one of the very best 240mm wides for ULF for around $700 by the time you've found a Copal 3S shutter ($300 with a bit of luck and $200 for the remount by SKGrimes). I actually sold my 210mm XL as soon as I had tested my 240mm. Yes, on occassion the slightly shorter focal lengh would be nice, but not $2000 more appealing. The 210mmXL is also a beast to lug around. I never carried it on me.