I saw a video of some great tips and such, in the video the guy use a pump up spray bottle to wet the panel after the filler was dry and sanded smooth so that he could use the strip lights over head to see what the panel might look like when painted, But he does not mention what was in the spray bottle.
What might be in the bottle? I am sure that what ever it is, it cant be water, or a gun wash as that would then be bad. ant thoughts.
I will try to link the video. I like watching this guys stuff. He is a character that I will say but great info in the videos, I went back and watch alot of the older stuff and found That I think he is worth subbing to.
https://www.youtube.com/watch?v=ClWF9vo3cZk
right around time mark 38:45