I always use matt varnish applied using a cocktail stick. If it needs to be held down in place I either use some Tamiya masking tape or anything small enough without the risk of damaging the etch like a small Humbrol paint tin. I’d leave it a good 24 hours before attempting to remove the weight or masking tape and afterwards I’d run around the edge with some more Matt varnish using a small paintbrush just to make sure it doesn’t come loose again anytime soon. Again, leaving it another 24hours or so before handling it.