Humbrol Maskol?

It's a liquid mask that can be painted onto the desired surface.  When it sets it forms a rubbery seal over the masked area (reasonably quickly).  Once you've finished you just peel the dried mask off.  I used it a couple of years ago and thought that it was really good for dealing with irregular areas that could be otherwise tricky to mask.  I'd avoid using your best brushes though as it can gum them up a bit if it's not cleaned quickly enough.  It smells a bit bad too but it's worth it I think!

Caution! Maskol is ammonia based and can eat an acrylic paint finish!

Ask me how I know that!

I have a pretty good idea but anyway, do tell.

I bought the stuff today and read the label. It says to clean the brush with a cellulose thinner. I've got tamiya x-20. Is that the cellulose stuff?

No? What is?

Cheers