What to do to sink cabinet so that water won't leak under it
Have you ever heard the phrase &quot;Lightning never strikes twice&quot;?
I think you're trying to prepare for an accident that is unlikely to happen again.
Sure, you can re-floor the cupboard, wedge it slightly at the back to ensure it slopes towards you, cut as best you can round the pipes, perhaps keep a fillet as insert round the back of the larger pipe, then gob it all in with silicone, including tanking the edges so the only way water can go is out the cupboard door. Don't use good glue &amp; don't run the silicone underneath except for a couple of stabilising dots, just in case you do ever need it out again.
Then wait to see if it ever happens again. For most people, two leaks in a lifetime would be a fair average… and in two different places, unless they have a poor fix the first time.
As mentioned in comments, you could tie a small piece of cloth round each &amp; see if one shows signs of damp &amp;/or mould… but your cold feed is likely to sweat (condensation will form) in humid weather, so that could be misleading.