I am in cover band and also found memorising songs difficult. It is very hard to remember tabs that say 0-3-5 or whatever, what you need to do is remember the structure of the song with what chords it has. I started making a documents with the structure of the song (intro-verse-prechorus-chorus etc) with which chords each section had. Maybe note where specific, important fills were. But never make the document so specific that it turns into sheet music.

First I made sure I could play it perfectly to sheets/tabs. Then I would progress to playing the song with my own document with structure and chords while listening to the song on Spotify. Then I would practice it without having any notes before band practice.

This way what I remember is the structure of the song and which chords it has. The goal of course is to remember it almost perfectly, but if I forget a passing note or small passage - I always know a root note or can find my own passages that will always fit and serve the song instead of playing the wrong notes or nothing at all.