Hi Kay,
here are 2 suggestions for counter enamel stands to support tubes during firing.
1) Insert a 1 mm thick stainless steel wire into a raw ceramik-tile on the right and left and, as shown in the picture, bend up a tip at the end of each wire. The tube rested on this tips during firing if the tube is also to be enamelled from the inside. The tube is first pushed over the left wire and then back onto the second.
So that the tile can be placed in the oven and taken out again, the tile must stand on small feet.

Stand 2 is simpler (center of picture). It is important that both, the stand in U-form and the wire are made of stainless steel. Diameter of the wire at least 1 mm.

Good success

Edmund

This is great! Thank you so much for the images!