Ummm... What? Are you asking for proof that this wasn't just a massive conspiracy, a "government coverup" that involved planting ships and bodies on the Delaware?

I'm kind of confused, it seems like you're saying "besides the ridiculous amount of evidence, what proof is there?"

I mean... Washington's forces started off on the West side of the Delaware, and ended up fighting a battle on the East side of the Delaware. How exactly would they have done so without crossing the Delaware?

The Battle of Trenton happened, and it happened at Trenton, New Jersey, on the East side of the Delaware. You might as well ask for proof, besides archaeological evidence and eyewitness testimony from both sides, that this battle occurred, if you're going to doubt evidence of the entire crossing.

If the crossing had never happened, the Battle of Trenton would have never happened, and reports of a US victory at Trenton would have been called into question and totally denied by the British (nevermind the actual people living in the area who heard/witnessed the battle.) Since this didn't happen, there is literally no reason at all to believe the crossing was a fictionary tale meant to boost morale.

I know I'm supposed to give sources for answers to the question, but this is such a ridiculous question I don't know if I should bother...

Edit:

The Winter Soldiers: The Battles for Trenton and Princeton by Richard Ketchum

Ketchum details this entire event, and even discusses a failed crossing to the South of Trenton. If this was propaganda only, it doesn't make sense for there to be multiple crossings, with some of them failing. But to even consider that, you have to get past the vast amounts of evidence and pure logic that show this event did indeed happen.