If we either side is going to rely on anecdotal claims like this, then we need to either have EVERYONE vote in person, so no military mail in ballots. Trump cannot mail in. Disabled people must appear in person, etc.
Or, in the alternative, we should come up with a way, with lots of verification, to allow people to vote electronically. You can access your tax records that way, and pay your taxes that way. You can look at your social security status that way. Certainly, there must be a way that voting could be set up to be done electronically and with confidence.
Trump cannot claim that any result unfavorable to him was caused by mail in voting fraud if in the meantime he has done nothing to allow verified electronic voting.